标签：style blog color ar div 代码 log sp 算法
鉴于最近在网上看到的二分查找算法非常复杂，细节太多，不容易理解，下面给出几个实现简洁，又容易理解的代码模版。
首先，让我们记住最基本的二分查找模版：
在有序数组A中查找key，如果找到，返回位置索引，否则，返回-1;
int BinarySearch(int A[], int n, int key) { int left = 0, right = n - 1; while (left <= right) { int mid = left + (right - left) / 2; if (A[mid] < key) { left = mid + 1; } else if (A[mid] > key) { right = mid - 1; } else {// A[mid] == key return mid; } } return -1; }
变种1：如果A有多个key元素，返回最大的，否则，返回-1
int BinarySearch(int A[], int n, int key) { int left = 0, right = n - 1; int result = -1; while (left <= right) { int mid = left + (right - left) / 2; if (A[mid] < key) { left = mid + 1; } else if (A[mid] > key) { right = mid - 1; } else {// A[mid] == key result = mid; left = mid + 1;//继续查找右半边 } } return result; }
变种2：如果A中有多个key元素，返回最小的，否则，返回-1
int BinarySearch(int A[], int n, int key) { int left = 0, right = n - 1; int result = -1; while (left <= right) { int mid = left + (right - left) / 2; if (A[mid] < key) { left = mid + 1; } else if (A[mid] > key) { right = mid - 1; } else {// A[mid] == key result = mid; right = mid - 1;// 继续查找左半边 } } return result; }
变种3：在有序数组A中，查找出最小的比key大的元素索引。
int BinarySearch(int A[], int n, int key) { if (A[n-1] < key) return -1; int left = 0, right = n - 1; while (left ！= right) { int mid = left + (right - left) / 2; if (A[mid] <= key) { left = mid + 1; } else { right = mid; } } return left; }
变种4:在有序数组A中，查找出最大的比k小的元素索引。
int BinarySearch(int A[], int n, int key) { if (A[0] > key) return -1; int left = 0, right = n - 1; while (left < right-1) { int mid = left + (right - left) / 2; if (A[mid] >= key) { right = mid - 1; } else { left = mid; } } if (A[right] < key) { return right; } else { return left; } }
标签：style blog color ar div 代码 log sp 算法
原文地址：http://www.cnblogs.com/xingzhg/p/3942221.html
