二分查找

C语言版：

#include<stdio.h>int BinarySearch(int *arr,int left,int right,int elem){    int min=left,max=right,mid;    while(min<max-1)    {        mid=min+(max-min)/2;        if(arr[mid]<=elem)        {            min=mid;        }else        {            max=mid;        }    }    if (arr[max]==elem){  return max;}else if(arr[min]==elem){return min;}else    {        return -1;    }}int BinarySearch2(int *arr,int left,int right,int elem){    int min=left,max=right,mid;    int p=-1;    while(min<=max)    {        mid=min+(max-min)/2;        if(arr[mid]<elem)        {            min=mid+1;        }else if(arr[mid]>elem)        {            max=mid-1;        }else        {            p=mid;            break;        }    }    return p;}int main(){    int arr[]={1,3,4,4,6,6,8,8,8,9,12,18};    int n=12;    int t=BinarySearch2(arr,0,n-1,9);    printf("%d\n",t);    return 0;}