查找算法——二分查找

/*******************************************************************************************
*Description 二分查找算法
*Author liaoxiongxiong
*Version 1.0
*Time 2018-04-28
*******************************************************************************************/

#include <stdio.h>

//二分查找，版本1
int BinarySearch1(int a[], int value, int n)
{
    int low, high, mid;
    low = 0;
    high = n-1;
    while(low<=high)
    {
        mid = (low+high)/2;
        if(a[mid] == value)
            return mid;
        if(a[mid]>value)
            high = mid-1;
        if(a[mid]<value)
            low = mid+1;
    }
    return -1;
}

//二分查找，版本2，递归版本
int BinarySearch2(int a[], int value, int low, int high)
{
    int mid = low+(high-low)/2;
    if(a[mid]==value)
        return mid;
    if(a[mid]>value)
        return BinarySearch2(a, value, low, mid-1);
    if(a[mid]<value)
        return BinarySearch2(a, value, mid+1, high);
}

//测试用例
int main()
{
    int a[]={0,1,2,3,4,5,6,7,8,9};
    int len = sizeof(a)/sizeof(a[0]);

    int x=2;   // 需要查找的元素

    int i = BinarySearch2(a, x, 0, len);
    if(i!=-1)
        printf("元素 %d 在第 %d 个位置\n",x,i+1);
    else
        printf("没有找到元素:%d\n",x);

    return 0;
}