二分查找

【二分查找】

针对有序数组，性能非常好。

【时间复杂度】

logn

【代码】

#include <stdio.h>#include <stdlib.h>//非递归实现二分查找int  BinarySearch1(int a[], int n, int key){int left, right;int mid;left = 0;right = n - 1;while(left <= right){mid = (left + right) / 2;if(key == a[mid])return mid;else if(key > a[mid])left = mid + 1;elseright = mid - 1;}return -1;}//递归实现二分查找int BinarySearch2(int a[], int left, int right, int key){if(left > right)return -1;else{int mid = (left + right) / 2;if(key == a[mid])return mid;else if(key < a[mid])BinarySearch2(a, left, mid - 1, key);elseBinarySearch2(a, mid + 1, right, key);}}int main(void){int a[13] = {3, 14, 27, 31, 39, 42, 55, 70, 74, 81, 85, 93, 98};int key = 81;int index1, index2;index1 = BinarySearch1(a, 13, key);index2 = BinarySearch2(a, 0, 13, key);printf("%d  %d\n", index1, index2);return 0;}