折半查找

二叉树看到线索二叉树就翻不动了，准备学一个简单地查找-二分查找。二分查找思想就是每次查找范围缩半，范围怎么缩的半？，我们通过改变数组的下标上限值或下限值来完成的，我们来看代码：

int binary_search (int *a,int n,int key)
{
    int low=0;
    int height = n;
    int mid=n/2;

    while(low <= height)
    {
            mid = (low + height)/2;
            if(a[mid]<key)        //使下限的值接近中间值
                low = mid +1; 
            else if(a[mid]>key)    //使上限的值接近中间值
                height = mid-1;
            else
                return mid;            //返回结果，即当上限与下限相等的时候
    }

    return 0;
}

验证代码：

#include <iostream>
using namespace std;
int binary_search (int *a,int n,int key);


int main()
{
    int a[10]={2,3,4,5,6,7,8,9,12,13};
    int search_num;
    for (int i = 0; i<10;i++)
    {
        cout<< a[i] <<endl;
    }
    cin>>search_num;

    cout<<binary_search (a,10,search_num)<<endl;
    getchar();
    getchar();
    return 0;
}