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### 前言   由于在前文的《[STL算法剖析](http://blog.csdn.net/chenhanzhun/article/details/39698523)》中,源码剖析非常多,不方便学习,也不方便以后复习,这里把这些算法进行归类,对他们单独的源码剖析进行讲解。本文介绍的STL算法中的find、search查找算法。在STL源码中有关算法的函数大部分在本文介绍,包含findand find_if、adjacent_find、search、search_n、lower_bound、upper_bound、equal_range、binary_search、find_first_of、find_end相关算法,下面对这些算法的源码进行了详细的剖析,并且适当给出应用例子,增加我们对其理解,方便我们使用这些算法。具体详见下面源码剖析。 ### 查找算法源码剖析 ~~~ // find and find_if. //查找区间[first,last)内元素第一个与value值相等的元素,并返回其位置 //其中find函数是采用默认的equality操作operator== //find_if是采用用户自行指定的操作pred //若find函数萃取出来的迭代器类型为输入迭代器input_iterator_tag,则调用此函数 template <class _InputIter, class _Tp> inline _InputIter find(_InputIter __first, _InputIter __last, const _Tp& __val, input_iterator_tag) {//若尚未到达区间的尾端,且未找到匹配的值,则继续查找 while (__first != __last && !(*__first == __val)) ++__first; //若找到匹配的值,则返回该位置 //若找不到,即到达区间尾端,此时first=last,则返回first return __first; } //若find_if函数萃取出来的迭代器类型为输入迭代器input_iterator_tag,则调用此函数 template <class _InputIter, class _Predicate> inline _InputIter find_if(_InputIter __first, _InputIter __last, _Predicate __pred, input_iterator_tag) {//若尚未到达区间的尾端,且未找到匹配的值,则继续查找 while (__first != __last && !__pred(*__first)) ++__first; //若找到匹配的值,则返回该位置 //若找不到,即到达区间尾端,此时first=last,则返回first return __first; } #ifdef __STL_CLASS_PARTIAL_SPECIALIZATION //若find函数萃取出来的迭代器类型为随机访问迭代器random_access_iterator_tag,则调用此函数 template <class _RandomAccessIter, class _Tp> _RandomAccessIter find(_RandomAccessIter __first, _RandomAccessIter __last, const _Tp& __val, random_access_iterator_tag) { typename iterator_traits<_RandomAccessIter>::difference_type __trip_count = (__last - __first) >> 2; for ( ; __trip_count > 0 ; --__trip_count) { if (*__first == __val) return __first; ++__first; if (*__first == __val) return __first; ++__first; if (*__first == __val) return __first; ++__first; if (*__first == __val) return __first; ++__first; } switch(__last - __first) { case 3: if (*__first == __val) return __first; ++__first; case 2: if (*__first == __val) return __first; ++__first; case 1: if (*__first == __val) return __first; ++__first; case 0: default: return __last; } } //若find_if函数萃取出来的迭代器类型为随机访问迭代器random_access_iterator_tag,则调用此函数 template <class _RandomAccessIter, class _Predicate> _RandomAccessIter find_if(_RandomAccessIter __first, _RandomAccessIter __last, _Predicate __pred, random_access_iterator_tag) { typename iterator_traits<_RandomAccessIter>::difference_type __trip_count = (__last - __first) >> 2; for ( ; __trip_count > 0 ; --__trip_count) { if (__pred(*__first)) return __first; ++__first; if (__pred(*__first)) return __first; ++__first; if (__pred(*__first)) return __first; ++__first; if (__pred(*__first)) return __first; ++__first; } switch(__last - __first) { case 3: if (__pred(*__first)) return __first; ++__first; case 2: if (__pred(*__first)) return __first; ++__first; case 1: if (__pred(*__first)) return __first; ++__first; case 0: default: return __last; } } #endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */ /*find函数功能:Returns an iterator to the first element in the range [first,last) that compares equal to val. If no such element is found, the function returns last. find函数原型: template <class InputIterator, class T> InputIterator find (InputIterator first, InputIterator last, const T& val); */ //find函数对外接口 template <class _InputIter, class _Tp> inline _InputIter find(_InputIter __first, _InputIter __last, const _Tp& __val) { __STL_REQUIRES(_InputIter, _InputIterator); __STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool, typename iterator_traits<_InputIter>::value_type, _Tp); //首先萃取出first迭代器的类型,根据迭代器的类型调用不同的函数 return find(__first, __last, __val, __ITERATOR_CATEGORY(__first)); } /*find_if函数功能:Returns an iterator to the first element in the range [first,last) for which pred returns true. If no such element is found, the function returns last. find_if函数原型: template <class InputIterator, class UnaryPredicate> InputIterator find_if (InputIterator first, InputIterator last, UnaryPredicate pred); */ //find_if 函数对外接口 template <class _InputIter, class _Predicate> inline _InputIter find_if(_InputIter __first, _InputIter __last, _Predicate __pred) { __STL_REQUIRES(_InputIter, _InputIterator); __STL_UNARY_FUNCTION_CHECK(_Predicate, bool, typename iterator_traits<_InputIter>::value_type); //首先萃取出first迭代器的类型,根据迭代器的类型调用不同的函数 return find_if(__first, __last, __pred, __ITERATOR_CATEGORY(__first)); } //find和find_if函数举例: /* #include <iostream> // std::cout #include <algorithm> // std::find_if #include <vector> // std::vector bool IsOdd (int i) { return ((i%2)==1); } int main () { std::vector<int> myvector; myvector.push_back(10); myvector.push_back(25); myvector.push_back(40); myvector.push_back(55); std::vector<int>::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd); std::cout << "The first odd value is " << *it << '\n'; // using std::find with vector and iterator: it = find (myvector.begin(), myvector.end(), 40); if (it != myvector.end()) std::cout << "Element found in myvector: " << *it << '\n'; else std::cout << "Element not found in myints\n"; return 0; } Output: The first odd value is 25 Element found in myvector: 40 */ // adjacent_find. //查找区间[first,last)内第一次重复的相邻元素 //若存在返回相邻元素的第一个元素位置 //若不存在返回last位置 /*该函数有两个版本:第一版本是默认操作operator==;第二版本是用户指定的二元操作pred 函数对外接口的原型: equality (1):默认操作是operator== template <class ForwardIterator> ForwardIterator adjacent_find (ForwardIterator first, ForwardIterator last); predicate (2):用户指定的二元操作pred template <class ForwardIterator, class BinaryPredicate> ForwardIterator adjacent_find (ForwardIterator first, ForwardIterator last, BinaryPredicate pred); */ //版本一:默认操作是operator== template <class _ForwardIter> _ForwardIter adjacent_find(_ForwardIter __first, _ForwardIter __last) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES(typename iterator_traits<_ForwardIter>::value_type, _EqualityComparable); /* 情况1:若输入区间为空,则直接返回尾端last; 情况2:若输入区间不为空,且存在相邻重复元素,则返回相邻元素的第一个元素的位置; 情况3:若输入区间不为空,但是不存在相邻重复元素,则直接返回尾端last; */ //情况1: if (__first == __last)//若输入区间为空 return __last;//直接返回last //情况2: _ForwardIter __next = __first;//定义当前位置的下一个位置(即当前元素的相邻元素) while(++__next != __last) {//若还没到达尾端,执行while循环 if (*__first == *__next)//相邻元素值相等,则找到相邻重复元素 return __first;//返回第一个元素的位置 __first = __next;//若暂时找不到,则继续找,直到到达区间尾端 } //情况3: return __last;//直接返回尾端last } //版本二:用户指定的二元操作pred //实现过程和版本一一样,只是判断规则不同 template <class _ForwardIter, class _BinaryPredicate> _ForwardIter adjacent_find(_ForwardIter __first, _ForwardIter __last, _BinaryPredicate __binary_pred) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_BINARY_FUNCTION_CHECK(_BinaryPredicate, bool, typename iterator_traits<_ForwardIter>::value_type, typename iterator_traits<_ForwardIter>::value_type); if (__first == __last) return __last; _ForwardIter __next = __first; while(++__next != __last) { //如果找到相邻元素符合用户指定条件,就返回第一元素位置 if (__binary_pred(*__first, *__next)) return __first; __first = __next; } return __last; } //adjacent_find函数举例: /* #include <iostream> // std::cout #include <algorithm> // std::adjacent_find #include <vector> // std::vector bool myfunction (int i, int j) { return (i==j); } int main () { int myints[] = {5,20,5,30,30,20,10,10,20}; std::vector<int> myvector (myints,myints+8); std::vector<int>::iterator it; // using default comparison: it = std::adjacent_find (myvector.begin(), myvector.end()); if (it!=myvector.end()) std::cout << "the first pair of repeated elements are: " << *it << '\n'; //using predicate comparison: it = std::adjacent_find (++it, myvector.end(), myfunction); if (it!=myvector.end()) std::cout << "the second pair of repeated elements are: " << *it << '\n'; return 0; } Output: the first pair of repeated elements are: 30 the second pair of repeated elements are: 10 */ // search. //在序列一[first1,last1)所涵盖的区间中,查找序列二[first2,last2)的首次出现点 //该查找函数有两个版本: //版本一:使用默认的equality操作operator== //版本二:用户根据需要自行指定操作规则 /*search函数功能:Searches the range [first1,last1) for the first occurrence of the sequence defined by [first2,last2), and returns an iterator to its first element, or last1 if no occurrences are found. search函数的原型: equality (1):版本一 template <class ForwardIterator1, class ForwardIterator2> ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2); predicate (2):版本二 template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> ForwardIterator1 search (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred); */ //版本一:使用默认的equality操作operator== template <class _ForwardIter1, class _ForwardIter2> _ForwardIter1 search(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2) { __STL_REQUIRES(_ForwardIter1, _ForwardIterator); __STL_REQUIRES(_ForwardIter2, _ForwardIterator); __STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool, typename iterator_traits<_ForwardIter1>::value_type, typename iterator_traits<_ForwardIter2>::value_type); // Test for empty ranges if (__first1 == __last1 || __first2 == __last2) return __first1; // Test for a pattern of length 1. _ForwardIter2 __tmp(__first2); ++__tmp; if (__tmp == __last2) return find(__first1, __last1, *__first2); // General case. _ForwardIter2 __p1, __p; __p1 = __first2; ++__p1; _ForwardIter1 __current = __first1; while (__first1 != __last1) {//若还没到达区间尾端 __first1 = find(__first1, __last1, *__first2);//查找*first2在区间[first1,last1)首次出现的位置 if (__first1 == __last1)//若在[first1,last1)中不存在*first2,即在[first1,last1)不存在子序列[first2,last2) return __last1;//则直接返回区间尾端 __p = __p1; __current = __first1; if (++__current == __last1)//若[first1,last1)只有一个元素,即序列[first1,last1)小于序列[first2,last2) return __last1;//不可能成为其子序列,返回last1 while (*__current == *__p) {//若两个序列相对应的值相同 if (++__p == __last2)//若序列[first2,last2)只有两个元素,且与序列一匹配 return __first1;//则返回匹配的首次位置 if (++__current == __last1)//若第一个序列小于第二个序列 return __last1;//返回last1 } ++__first1; } return __first1; } //版本二:用户根据需要自行指定操作规则 template <class _ForwardIter1, class _ForwardIter2, class _BinaryPred> _ForwardIter1 search(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2, _BinaryPred __predicate) { __STL_REQUIRES(_ForwardIter1, _ForwardIterator); __STL_REQUIRES(_ForwardIter2, _ForwardIterator); __STL_BINARY_FUNCTION_CHECK(_BinaryPred, bool, typename iterator_traits<_ForwardIter1>::value_type, typename iterator_traits<_ForwardIter2>::value_type); // Test for empty ranges if (__first1 == __last1 || __first2 == __last2) return __first1; // Test for a pattern of length 1. _ForwardIter2 __tmp(__first2); ++__tmp; if (__tmp == __last2) { while (__first1 != __last1 && !__predicate(*__first1, *__first2)) ++__first1; return __first1; } // General case. _ForwardIter2 __p1, __p; __p1 = __first2; ++__p1; _ForwardIter1 __current = __first1; while (__first1 != __last1) { while (__first1 != __last1) { if (__predicate(*__first1, *__first2)) break; ++__first1; } while (__first1 != __last1 && !__predicate(*__first1, *__first2)) ++__first1; if (__first1 == __last1) return __last1; __p = __p1; __current = __first1; if (++__current == __last1) return __last1; while (__predicate(*__current, *__p)) { if (++__p == __last2) return __first1; if (++__current == __last1) return __last1; } ++__first1; } return __first1; } // search_n. Search for __count consecutive copies of __val. //在序列[first,last)查找连续count个符合条件值value元素的位置 //该查找函数有两个版本: //版本一:使用默认的equality操作operator== //版本二:用户根据需要自行指定操作规则 /*search_n函数功能:Searches the range [first,last) for a sequence of count elements, each comparing equal to val (or for which pred returns true). search_n函数的原型: equality (1):版本一 template <class ForwardIterator, class Size, class T> ForwardIterator search_n (ForwardIterator first, ForwardIterator last, Size count, const T& val); predicate (2):版本二 template <class ForwardIterator, class Size, class T, class BinaryPredicate> ForwardIterator search_n ( ForwardIterator first, ForwardIterator last, Size count, const T& val, BinaryPredicate pred ); */ //版本一:使用默认的equality操作operator== template <class _ForwardIter, class _Integer, class _Tp> _ForwardIter search_n(_ForwardIter __first, _ForwardIter __last, _Integer __count, const _Tp& __val) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES(typename iterator_traits<_ForwardIter>::value_type, _EqualityComparable); __STL_REQUIRES(_Tp, _EqualityComparable); if (__count <= 0) return __first; else {//首先查找value第一次出现的位置 __first = find(__first, __last, __val); while (__first != __last) {//若出现的位置不是区间尾端 _Integer __n = __count - 1;//更新个数,下面只需查找n=count-1个连续相同value即可 _ForwardIter __i = __first; ++__i;//从当前位置的下一个位置开始查找 //若没有到达区间尾端,且个数n大于0,且区间元素与value值相等 while (__i != __last && __n != 0 && *__i == __val) { ++__i;//继续查找 --__n;//减少查找的次数,因为已经找到value再次出现 } if (__n == 0)//若区间尚未到达尾端,但是count个value已经查找到 return __first;//则输出查找到的首次出现value的位置 else __first = find(__i, __last, __val);//若尚未找到连续count个value值的位置,则找出value下次出现的位置,并准备下一次while循环 } return __last; } } //版本二:用户根据需要自行指定操作规则 template <class _ForwardIter, class _Integer, class _Tp, class _BinaryPred> _ForwardIter search_n(_ForwardIter __first, _ForwardIter __last, _Integer __count, const _Tp& __val, _BinaryPred __binary_pred) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_BINARY_FUNCTION_CHECK(_BinaryPred, bool, typename iterator_traits<_ForwardIter>::value_type, _Tp); if (__count <= 0) return __first; else { while (__first != __last) { if (__binary_pred(*__first, __val)) break; ++__first; } while (__first != __last) { _Integer __n = __count - 1; _ForwardIter __i = __first; ++__i; while (__i != __last && __n != 0 && __binary_pred(*__i, __val)) { ++__i; --__n; } if (__n == 0) return __first; else { while (__i != __last) { if (__binary_pred(*__i, __val)) break; ++__i; } __first = __i; } } return __last; } } //search和search_n函数举例: /* #include <iostream> // std::cout #include <algorithm> // std::search_n #include <vector> // std::vector bool mypredicate (int i, int j) { return (i==j); } int main () { int myints[]={10,20,30,30,20,10,10,20}; std::vector<int> myvector (myints,myints+8); std::vector<int>::iterator it; // using default comparison: it = std::search_n (myvector.begin(), myvector.end(), 2, 30); if (it!=myvector.end()) std::cout << "two 30s found at position " << (it-myvector.begin()) << '\n'; else std::cout << "match not found\n"; // using predicate comparison: it = std::search_n (myvector.begin(), myvector.end(), 2, 10, mypredicate); if (it!=myvector.end()) std::cout << "two 10s found at position " << int(it-myvector.begin()) << '\n'; else std::cout << "match not found\n"; int needle1[] = {10,20}; // using default comparison: it = std::search (myvector.begin(), myvector.end(), needle1, needle1+2); if (it!=myvector.end()) std::cout << "needle1 found at position " << (it-myvector.begin()) << '\n'; else std::cout << "needle1 not found\n"; // using predicate comparison: int needle2[] = {30,20,10}; it = std::search (myvector.begin(), myvector.end(), needle2, needle2+3, mypredicate); if (it!=myvector.end()) std::cout << "needle2 found at position " << (it-myvector.begin()) << '\n'; else std::cout << "needle2 not found\n"; return 0; } Output: two 30s found at position 2 two 10s found at position 5 needle1 found at position 0 needle2 found at position 3 */ // Binary search (lower_bound, upper_bound, equal_range, binary_search). template <class _ForwardIter, class _Tp, class _Distance> _ForwardIter __lower_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Distance*) { _Distance __len = 0; distance(__first, __last, __len);//求取整个区间的长度len _Distance __half; _ForwardIter __middle;//定义区间的中间迭代器 while (__len > 0) {//若区间不为空,则在区间[first,last)开始查找value值 __half = __len >> 1;//向右移一位,相当于除以2,即取区间的中间值 __middle = __first;//middle初始化为区间的起始位置 advance(__middle, __half);//middle向后移half位,此时middle为区间的中间值 if (*__middle < __val) {//将value值与中间值比较,即是二分查找,若中间值小于value,则继续查找右半部分 //下面两行令first指向middle的下一个位置 __first = __middle; ++__first; __len = __len - __half - 1;//调整查找区间的长度 } else __len = __half;//否则查找左半部分 } return __first; } //在已排序区间[first,last)查找value值 //若该区间存在与value相等的元素,则返回指向第一个与value相等的迭代器 //若该区间不存在与value相等的元素,则返回指向第一个不小于value值的迭代器 //若该区间的任何元素都比value值小,则返回last /* 函数功能:Returns an iterator pointing to the first element in the range [first,last) which does not compare less than val. 函数原型: default (1) :版本一采用operator<比较 template <class ForwardIterator, class T> ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val); custom (2) :版本二采用仿函数comp比较规则 template <class ForwardIterator, class T, class Compare> ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val, Compare comp); */ //版本一 template <class _ForwardIter, class _Tp> inline _ForwardIter lower_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_REQUIRES(_Tp, _LessThanComparable); return __lower_bound(__first, __last, __val, __DISTANCE_TYPE(__first)); } template <class _ForwardIter, class _Tp, class _Compare, class _Distance> _ForwardIter __lower_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp, _Distance*) { _Distance __len = 0; distance(__first, __last, __len);//求取整个区间的长度len _Distance __half; _ForwardIter __middle;//定义区间的中间迭代器 while (__len > 0) {//若区间不为空,则在区间[first,last)开始查找value值 __half = __len >> 1;//向右移一位,相当于除以2,即取区间的中间值 __middle = __first;//middle初始化为区间的起始位置 advance(__middle, __half);//middle向后移half位,此时middle为区间的中间值 if (__comp(*__middle, __val)) {//若comp判断为true,则继续在右半部分查找 //下面两行令first指向middle的下一个位置 __first = __middle; ++__first; __len = __len - __half - 1;//调整查找区间的长度 } else __len = __half;//否则查找左半部分 } return __first; } //版本二: template <class _ForwardIter, class _Tp, class _Compare> inline _ForwardIter lower_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp); return __lower_bound(__first, __last, __val, __comp, __DISTANCE_TYPE(__first)); } template <class _ForwardIter, class _Tp, class _Distance> _ForwardIter __upper_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Distance*) { _Distance __len = 0; distance(__first, __last, __len);//求取整个区间的长度len _Distance __half; _ForwardIter __middle;//定义区间的中间迭代器 while (__len > 0) {//若区间不为空,则在区间[first,last)开始查找value值 __half = __len >> 1;//向右移一位,相当于除以2,即取区间的中间值 __middle = __first;//middle初始化为区间的起始位置 advance(__middle, __half);//middle向后移half位,此时middle为区间的中间值 if (__val < *__middle)//若value小于中间元素值 __len = __half;//查找左半部分 else { //下面两行令first指向middle的下一个位置 __first = __middle; ++__first; __len = __len - __half - 1;//更新len的值 } } return __first; } //在已排序区间[first,last)查找value值 //返回大于value值的第一个元素的迭代器 /* 函数功能:Returns an iterator pointing to the first element in the range [first,last) which compares greater than val. 函数原型: default (1) :版本一采用operator<比较 template <class ForwardIterator, class T> ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val); custom (2) :版本二采用仿函数comp比较规则 template <class ForwardIterator, class T, class Compare> ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val, Compare comp); */ //版本一 template <class _ForwardIter, class _Tp> inline _ForwardIter upper_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_REQUIRES(_Tp, _LessThanComparable); return __upper_bound(__first, __last, __val, __DISTANCE_TYPE(__first)); } template <class _ForwardIter, class _Tp, class _Compare, class _Distance> _ForwardIter __upper_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp, _Distance*) { _Distance __len = 0; distance(__first, __last, __len); _Distance __half; _ForwardIter __middle; while (__len > 0) { __half = __len >> 1; __middle = __first; advance(__middle, __half); if (__comp(__val, *__middle)) __len = __half; else { __first = __middle; ++__first; __len = __len - __half - 1; } } return __first; } //版本二 template <class _ForwardIter, class _Tp, class _Compare> inline _ForwardIter upper_bound(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp); return __upper_bound(__first, __last, __val, __comp, __DISTANCE_TYPE(__first)); } //函数举例 /* #include <iostream> // std::cout #include <algorithm> // std::lower_bound, std::upper_bound, std::sort #include <vector> // std::vector int main () { int myints[] = {10,20,30,30,20,10,10,20}; std::vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20 std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30 std::vector<int>::iterator low,up; low=std::lower_bound (v.begin(), v.end(), 20); // ^ up= std::upper_bound (v.begin(), v.end(), 20); // ^ std::cout << "lower_bound at position " << (low- v.begin()) << '\n'; std::cout << "upper_bound at position " << (up - v.begin()) << '\n'; return 0; } Output: lower_bound at position 3 upper_bound at position 6 */ template <class _ForwardIter, class _Tp, class _Distance> pair<_ForwardIter, _ForwardIter> __equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Distance*) { _Distance __len = 0; distance(__first, __last, __len);//计算区间的长度len _Distance __half; _ForwardIter __middle, __left, __right; while (__len > 0) {//若区间非空 __half = __len >> 1;//len右移一位,相等于除以2,即half为区间的长度的一半 __middle = __first;//初始化middle的值 advance(__middle, __half);//前进middle位置,使其指向区间中间位置 if (*__middle < __val) {//若指定元素value大于中间元素值,则在右半部分继续查找 //下面两行使first指向middle的下一个位置,即右半区间的起始位置 __first = __middle; ++__first; __len = __len - __half - 1;//更新待查找区间的长度 } else if (__val < *__middle)//若指定元素value小于中间元素值,则在左半部分继续查找 __len = __half;//更新待查找区间的长度 else {//若指定元素value等于中间元素值 //在前半部分找lower_bound位置 __left = lower_bound(__first, __middle, __val); advance(__first, __len); //在后半部分找upper_bound __right = upper_bound(++__middle, __first, __val); return pair<_ForwardIter, _ForwardIter>(__left, __right);//返回pair对象,第一个迭代器为left,第二个迭代器为right } } return pair<_ForwardIter, _ForwardIter>(__first, __first); } //查找区间与value相等的相邻重复元素的起始位置和结束位置 //注意:[first,last)是已排序,思想还是采用二分查找法 //同样也有两个版本 /* 函数功能:Returns the bounds of the subrange that includes all the elements of the range [first,last) with values equivalent to val. 函数原型: default (1) :版本一默认operator< template <class ForwardIterator, class T> pair<ForwardIterator,ForwardIterator> equal_range (ForwardIterator first, ForwardIterator last, const T& val); custom (2) :版本二采用仿函数comp template <class ForwardIterator, class T, class Compare> pair<ForwardIterator,ForwardIterator> equal_range (ForwardIterator first, ForwardIterator last, const T& val, Compare comp); */ //版本一 template <class _ForwardIter, class _Tp> inline pair<_ForwardIter, _ForwardIter> equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_REQUIRES(_Tp, _LessThanComparable); return __equal_range(__first, __last, __val, __DISTANCE_TYPE(__first)); } template <class _ForwardIter, class _Tp, class _Compare, class _Distance> pair<_ForwardIter, _ForwardIter> __equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp, _Distance*) { _Distance __len = 0; distance(__first, __last, __len); _Distance __half; _ForwardIter __middle, __left, __right; while (__len > 0) { __half = __len >> 1; __middle = __first; advance(__middle, __half); if (__comp(*__middle, __val)) { __first = __middle; ++__first; __len = __len - __half - 1; } else if (__comp(__val, *__middle)) __len = __half; else { __left = lower_bound(__first, __middle, __val, __comp); advance(__first, __len); __right = upper_bound(++__middle, __first, __val, __comp); return pair<_ForwardIter, _ForwardIter>(__left, __right); } } return pair<_ForwardIter, _ForwardIter>(__first, __first); } //版本二 template <class _ForwardIter, class _Tp, class _Compare> inline pair<_ForwardIter, _ForwardIter> equal_range(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp); return __equal_range(__first, __last, __val, __comp, __DISTANCE_TYPE(__first)); } //equal_range函数举例: /* #include <iostream> // std::cout #include <algorithm> // std::equal_range, std::sort #include <vector> // std::vector bool mygreater (int i,int j) { return (i>j); } int main () { int myints[] = {10,20,30,30,20,10,10,20}; std::vector<int> v(myints,myints+8); // 10 20 30 30 20 10 10 20 std::pair<std::vector<int>::iterator,std::vector<int>::iterator> bounds; // using default comparison: std::sort (v.begin(), v.end()); // 10 10 10 20 20 20 30 30 bounds=std::equal_range (v.begin(), v.end(), 20); // ^ ^ std::cout << "bounds at positions " << (bounds.first - v.begin()); std::cout << " and " << (bounds.second - v.begin()) << '\n'; // using "mygreater" as comp: std::sort (v.begin(), v.end(), mygreater); // 30 30 20 20 20 10 10 10 bounds=std::equal_range (v.begin(), v.end(), 20, mygreater); // ^ ^ std::cout << "bounds at positions " << (bounds.first - v.begin()); std::cout << " and " << (bounds.second - v.begin()) << '\n'; return 0; } Output: bounds at positions 3 and 6 bounds at positions 2 and 5 */ //二分查找法 //注意:[first,last)是已排序 //同样也有两个版本 /* 函数功能:Returns true if any element in the range [first,last) is equivalent to val, and false otherwise. 函数原型: default (1) :版本一默认operator< template <class ForwardIterator, class T> bool binary_search (ForwardIterator first, ForwardIterator last, const T& val); custom (2) :版本二采用仿函数comp template <class ForwardIterator, class T, class Compare> bool binary_search (ForwardIterator first, ForwardIterator last, const T& val, Compare comp); */ template <class _ForwardIter, class _Tp> bool binary_search(_ForwardIter __first, _ForwardIter __last, const _Tp& __val) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_REQUIRES(_Tp, _LessThanComparable); _ForwardIter __i = lower_bound(__first, __last, __val);//调用二分查找函数,并返回不小于value值的第一个迭代器位置i return __i != __last && !(__val < *__i); } template <class _ForwardIter, class _Tp, class _Compare> bool binary_search(_ForwardIter __first, _ForwardIter __last, const _Tp& __val, _Compare __comp) { __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_SAME_TYPE(_Tp, typename iterator_traits<_ForwardIter>::value_type); __STL_BINARY_FUNCTION_CHECK(_Compare, bool, _Tp, _Tp); _ForwardIter __i = lower_bound(__first, __last, __val, __comp);//调用二分查找函数,并返回不小于value值的第一个迭代器位置i return __i != __last && !__comp(__val, *__i); } // find_first_of, with and without an explicitly supplied comparison function. //以[first2,last2)区间内的某些元素为查找目标,寻找他们在[first1,last1)区间首次出现的位置 //find_first_of函数有两个版本: //版本一:提供默认的equality操作operator== //版本二:提供用户自行指定的操作规则comp /* 函数功能:Returns an iterator to the first element in the range [first1,last1) that matches any of the elements in [first2,last2). If no such element is found, the function returns last1. 函数原型: equality (1):版本一 template <class ForwardIterator1, class ForwardIterator2> ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2); predicate (2):版本二 template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> ForwardIterator1 find_first_of (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred); */ //版本一:提供默认的equality操作operator== template <class _InputIter, class _ForwardIter> _InputIter find_first_of(_InputIter __first1, _InputIter __last1, _ForwardIter __first2, _ForwardIter __last2) { __STL_REQUIRES(_InputIter, _InputIterator); __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool, typename iterator_traits<_InputIter>::value_type, typename iterator_traits<_ForwardIter>::value_type); for ( ; __first1 != __last1; ++__first1) //若序列一不为空,则遍历序列一,每次指定一个元素 //以下,根据序列二的每个元素 for (_ForwardIter __iter = __first2; __iter != __last2; ++__iter) if (*__first1 == *__iter)//若序列一的元素等于序列二的元素,则表示找到 return __first1;//返回找到的位置 return __last1;//否则没找到 } //版本二:提供用户自行指定的操作规则comp template <class _InputIter, class _ForwardIter, class _BinaryPredicate> _InputIter find_first_of(_InputIter __first1, _InputIter __last1, _ForwardIter __first2, _ForwardIter __last2, _BinaryPredicate __comp) { __STL_REQUIRES(_InputIter, _InputIterator); __STL_REQUIRES(_ForwardIter, _ForwardIterator); __STL_BINARY_FUNCTION_CHECK(_BinaryPredicate, bool, typename iterator_traits<_InputIter>::value_type, typename iterator_traits<_ForwardIter>::value_type); for ( ; __first1 != __last1; ++__first1) for (_ForwardIter __iter = __first2; __iter != __last2; ++__iter) if (__comp(*__first1, *__iter)) return __first1; return __last1; } //find_first_of函数举例: /* #include <iostream> // std::cout #include <algorithm> // std::find_first_of #include <vector> // std::vector #include <cctype> // std::tolower bool comp_case_insensitive (char c1, char c2) { return (std::tolower(c1)==std::tolower(c2)); } int main () { int mychars[] = {'a','b','c','A','B','C'}; std::vector<char> haystack (mychars,mychars+6); std::vector<char>::iterator it; int needle[] = {'A','B','C'}; // using default comparison: it = find_first_of (haystack.begin(), haystack.end(), needle, needle+3); if (it!=haystack.end()) std::cout << "The first match is: " << *it << '\n'; // using predicate comparison: it = find_first_of (haystack.begin(), haystack.end(), needle, needle+3, comp_case_insensitive); if (it!=haystack.end()) std::cout << "The first match is: " << *it << '\n'; return 0; } Output: The first match is: A The first match is: a */ // find_end, with and without an explicitly supplied comparison function. // Search [first2, last2) as a subsequence in [first1, last1), and return // the *last* possible match. Note that find_end for bidirectional iterators // is much faster than for forward iterators. // find_end for forward iterators. //若萃取出来的迭代器类型为正向迭代器forward_iterator_tag,则调用此函数 template <class _ForwardIter1, class _ForwardIter2> _ForwardIter1 __find_end(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2, forward_iterator_tag, forward_iterator_tag) { if (__first2 == __last2)//若第二个区间为空 return __last1;//则直接返回第一个区间的尾端 else { _ForwardIter1 __result = __last1; while (1) { //以下利用search函数查找出某个子序列的首次出现点;若找不到直接返回last1 _ForwardIter1 __new_result = search(__first1, __last1, __first2, __last2); if (__new_result == __last1)//若返回的位置为尾端,则表示没找到 return __result;//返回last1 else {//若在[first1,last1)中找到[first2,last2)首次出现的位置,继续准备下一次查找 __result = __new_result;//更新返回的位置 __first1 = __new_result;//更新查找的起始位置 ++__first1;//确定正确查找起始位置 } } } } //版本二:指定规则 template <class _ForwardIter1, class _ForwardIter2, class _BinaryPredicate> _ForwardIter1 __find_end(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2, forward_iterator_tag, forward_iterator_tag, _BinaryPredicate __comp) { if (__first2 == __last2) return __last1; else { _ForwardIter1 __result = __last1; while (1) { _ForwardIter1 __new_result = search(__first1, __last1, __first2, __last2, __comp); if (__new_result == __last1) return __result; else { __result = __new_result; __first1 = __new_result; ++__first1; } } } } // find_end for bidirectional iterators. Requires partial specialization. #ifdef __STL_CLASS_PARTIAL_SPECIALIZATION //若萃取出来的迭代器类型为双向迭代器bidirectional_iterator_tag,则调用此函数 template <class _BidirectionalIter1, class _BidirectionalIter2> _BidirectionalIter1 __find_end(_BidirectionalIter1 __first1, _BidirectionalIter1 __last1, _BidirectionalIter2 __first2, _BidirectionalIter2 __last2, bidirectional_iterator_tag, bidirectional_iterator_tag) { __STL_REQUIRES(_BidirectionalIter1, _BidirectionalIterator); __STL_REQUIRES(_BidirectionalIter2, _BidirectionalIterator); //利用反向迭代器很快就可以找到 typedef reverse_iterator<_BidirectionalIter1> _RevIter1; typedef reverse_iterator<_BidirectionalIter2> _RevIter2; _RevIter1 __rlast1(__first1); _RevIter2 __rlast2(__first2); //查找时将序列一和序列二逆方向 _RevIter1 __rresult = search(_RevIter1(__last1), __rlast1, _RevIter2(__last2), __rlast2); if (__rresult == __rlast1)//表示没找到 return __last1; else {//找到了 _BidirectionalIter1 __result = __rresult.base();//转会正常迭代器 advance(__result, -distance(__first2, __last2));//调整回到子序列的起始位置 return __result; } } //版本二:指定规则comp template <class _BidirectionalIter1, class _BidirectionalIter2, class _BinaryPredicate> _BidirectionalIter1 __find_end(_BidirectionalIter1 __first1, _BidirectionalIter1 __last1, _BidirectionalIter2 __first2, _BidirectionalIter2 __last2, bidirectional_iterator_tag, bidirectional_iterator_tag, _BinaryPredicate __comp) { __STL_REQUIRES(_BidirectionalIter1, _BidirectionalIterator); __STL_REQUIRES(_BidirectionalIter2, _BidirectionalIterator); typedef reverse_iterator<_BidirectionalIter1> _RevIter1; typedef reverse_iterator<_BidirectionalIter2> _RevIter2; _RevIter1 __rlast1(__first1); _RevIter2 __rlast2(__first2); _RevIter1 __rresult = search(_RevIter1(__last1), __rlast1, _RevIter2(__last2), __rlast2, __comp); if (__rresult == __rlast1) return __last1; else { _BidirectionalIter1 __result = __rresult.base(); advance(__result, -distance(__first2, __last2)); return __result; } } #endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */ // Dispatching functions for find_end. //find_end函数有两个版本: //版本一:提供默认的equality操作operator== //版本二:提供用户自行指定的操作规则comp //注意:这里也有偏特化的知识 /*函数功能:Searches the range [first1,last1) for the last occurrence of the sequence defined by [first2,last2), and returns an iterator to its first element, or last1 if no occurrences are found. 函数原型: equality (1):版本一 template <class ForwardIterator1, class ForwardIterator2> ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2); predicate (2):版本二 template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate> ForwardIterator1 find_end (ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred); */ //对外接口的版本一 template <class _ForwardIter1, class _ForwardIter2> inline _ForwardIter1 find_end(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2) { __STL_REQUIRES(_ForwardIter1, _ForwardIterator); __STL_REQUIRES(_ForwardIter2, _ForwardIterator); __STL_REQUIRES_BINARY_OP(_OP_EQUAL, bool, typename iterator_traits<_ForwardIter1>::value_type, typename iterator_traits<_ForwardIter2>::value_type); //首先通过iterator_traits萃取出first1和first2的迭代器类型 //根据不同的迭代器类型调用不同的函数 return __find_end(__first1, __last1, __first2, __last2, __ITERATOR_CATEGORY(__first1), __ITERATOR_CATEGORY(__first2)); } //对外接口的版本一 template <class _ForwardIter1, class _ForwardIter2, class _BinaryPredicate> inline _ForwardIter1 find_end(_ForwardIter1 __first1, _ForwardIter1 __last1, _ForwardIter2 __first2, _ForwardIter2 __last2, _BinaryPredicate __comp) { __STL_REQUIRES(_ForwardIter1, _ForwardIterator); __STL_REQUIRES(_ForwardIter2, _ForwardIterator); __STL_BINARY_FUNCTION_CHECK(_BinaryPredicate, bool, typename iterator_traits<_ForwardIter1>::value_type, typename iterator_traits<_ForwardIter2>::value_type); //首先通过iterator_traits萃取出first1和first2的迭代器类型 //根据不同的迭代器类型调用不同的函数 return __find_end(__first1, __last1, __first2, __last2, __ITERATOR_CATEGORY(__first1), __ITERATOR_CATEGORY(__first2), __comp); } //find_end函数举例: /* #include <iostream> // std::cout #include <algorithm> // std::find_end #include <vector> // std::vector bool myfunction (int i, int j) { return (i==j); } int main () { int myints[] = {1,2,3,4,5,1,2,3,4,5}; std::vector<int> haystack (myints,myints+10); int needle1[] = {1,2,3}; // using default comparison: std::vector<int>::iterator it; it = std::find_end (haystack.begin(), haystack.end(), needle1, needle1+3); if (it!=haystack.end()) std::cout << "needle1 last found at position " << (it-haystack.begin()) << '\n'; int needle2[] = {4,5,1}; // using predicate comparison: it = std::find_end (haystack.begin(), haystack.end(), needle2, needle2+3, myfunction); if (it!=haystack.end()) std::cout << "needle2 last found at position " << (it-haystack.begin()) << '\n'; return 0; } Output: needle1 found at position 5 needle2 found at position 3 */ ~~~ 参考资料: 《STL源码剖析》侯捷