在排序的数组中二分查找一个元素，返回在数组中它第一次出现的位置

可以参考stl中lower_bound算法。

 

 

#include "stdafx.h"#include <iostream>using namespace std;int  BinSearchFirst(int arr[], int begin, int end, int target){int mid = 0;int half = 0;int len = end - begin;while (len > 0){half = len>>1;mid = begin + half;if (arr[mid] < target){begin = mid + 1;len = len - half - 1;}elselen = half;}return begin;}int main(){int arr[] = {4, 10, 10, 30, 40, 100};int pos = BinSearchFirst(arr, 0, sizeof(arr) / sizeof(*arr), 10);cout<<pos<<endl;}