## 二分查找 前提条件：数组有序 ``` template <typename T> int binarySearch(vector<T>& data, int l, int r, T target) { if (l > r) return -1; int mid = l + (r - l) / 2; if (target == data[mid]) return mid; else if (target < data[mid]) return binarySearch(data, l, mid - 1, target); else return binarySearch(data, mid + 1, r, target); } template <typename T> int binarySearch(vector<T>& data, T target) { return binarySearch(data, 0, data.size()-1, target); } ```