算法实验-实验一：二分查找法

#include <bits/stdc++.h>

using namespace std;
//二分查找递归算法
int binary_search(int *a,int begin,int end,int x){
    if(begin>end)
        return -1;
    int mid = (begin+end)/2;
    if(x==a[mid])
        return mid;
    else if(x<a[mid])
        return binary_search(a,begin,mid-1,x);
    else
        return binary_search(a,mid+1,end,x);
}
//判断数组a是否有序
bool judge(int *a,int n){
    bool flag = true;
    for(int i=0;i<n-1;i++){
        if(a[i]>a[i+1]){
            flag = false;
            break;
        }
    }
    return flag;
}
//快速排序
int patartion(int *a,int left,int right){
    int x = a[left];
    int l = left;
    int r = right+1;
    while(true){
        while(a[++l]<x&&l<r);
        while(a[--r]>x);
        if(l>=r)
            break;
        swap(a[l],a[r]);
    }
    a[left] = a[r];
    a[r] = x;
    return r;
}

void Quick(int *a,int begin,int end){
    if(begin>end)
        return;
    else{
        int p = patartion(a,begin,end);
        Quick(a,begin,p-1);
        Quick(a,p+1,end);
    }
}

int main()
{
    int n;
    int x;
    printf("输入待查找数组的大小：");
    scanf("%d",&n);
    int a[n];
    for(int i=0;i<n;i++){
        scanf("%d",&a[i]);
    }
    if(!judge(a,n))//如果数组无序，则利用快速排序给数组排序
        Quick(a,0,n);
    //for(int i=0;i<n;i++)
    //    printf("%d ",a[i]);
    printf("输入要查找的元素：");
    scanf("%d",&x);
    int pos = binary_search(a,0,n,x);
    if(pos==-1)
        printf("not find!\n");
    else
        printf("%d\n",pos);
    return 0;
}