折半查找

折半查找

#include<time.h>
#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
const int n=10;
int Erfen(int *a,int n,int key)//开始查找
{
    int low=0;
    int high=n-1;
    int middle;
    while(low<=high)
    {
        middle=(low+high)/2;
        if(a[middle]==key) return middle;
        else if(a[middle]>key) high=middle-1;
        else low=middle+1;
    }
    return -1;
}
int main()
{

    int a[n],key;
    key=6;//关键字自定义
    clock_t start,end;
    start=clock();//开始计时

    srand(time(0));  //种子 
    cout<<"key= "<<key<<endl;

    for(int i=0;i<n;i++)
    {
        a[i]=rand()%(n-2)+1;//产生随机数，并给数组
        cout<<a[i]<<" ";
    }
    cout<<endl;

    sort(a,a+n);
    cout<<"排序后的数组："<<endl;
    for(i=0;i<n;i++)
    {
        cout<<a[i]<<" ";
    }
    cout<<endl;
    int temp=Erfen(a,n,key);//查找
    if(temp==-1) cout<<"no found"<<endl;
    else cout<<"数字所在位置的数组下标是："<<temp<<endl;

    end=clock();//计时结束（一般时间太短，显示为0.00000等）
    cout<<"time: ";
    printf("%6.5f\n",end-start);
    return 0;
}