二分查找算法

通过改变边界位置来进行查找的方法，代码如下：

 

#include <iostream>

using namespace std;


int search(int *p,int length,int key);
int search1(int *p,int length,int key);

int main()
{
    cout << "Hello world!" << endl;
    int a[] = {1,2,3,4,5,6,7,8,8,8,9,10,11,12,13,14};
    int len = sizeof(a)/sizeof(int);
    int pos = search1(a,len,8);
    cout << pos << endl;
    return 0;
}

int search1(int *p,int length,int key)
{
    int left=0;
    int right=length-1;
    while(left<=right)
    {
        int mid = (left+right)/2;
        if(p[mid]>=key)
        {
            right = mid-1;
        }else
        {
            left = mid+1;
        }
    }
    if(left<length && p[left]==key)
        return left;
    return -1;
}


int search(int *p,int length,int key)
{
    int left=0;
    int right = length -1;

    while(left<=right)
    {
        int mid = (left+right)/2;
        if(p[mid]==key)
        {
            return mid;
        }
        if(p[mid] > key)
        {
            right = mid+1;
        }
        if(p[mid]<key)
        {
            left=mid-1;
        }
    }
    return -1;
}