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;
}