随机选择算法-来自 胡凡 曾磊的《算法笔记》

#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <algorithm>
#include <math.h>
using namespace std;
const int maxn = 100010;
int A[maxn], n;
int randPartition(int A[], int left, int right){
    int p = (round(1.0*rand()/RAND_MAX*(right - left) + left));
    swap(A[p],A[left]);
    int temp = A[left];
    while(left < right){
        while(left<right&&A[right]>temp) right--;
        A[left] = A[right];
        while(left<right&&A[left]<=temp) left++;
        A[right] = A[left];
    }
    A[left] = temp;
    return left;
}
//随机选择算法
void randSelect(int A[], int left, int right, int K){
    if(left==right) return;
    int p = randPartition(A,left,right);
    int M = p - left + 1;
    if(K==M) return;
    if(K<M){
        randSelect(A,left,p-1,K);
    }else{
        randSelect(A,p+1,right,K-M);
    }
}

int main(){
    srand((unsigned)time(NULL));
    int sum=0,sum1=0;
    scanf("%d",&n);
    for(int i=0; i<n; i++){
        scanf("%d", &A[i]);
        sum+=A[i];
    }
    randSelect(A,0,n-1,n/2);
    for(int i=0; i<n/2; i++){
        sum1+=A[i];
    }
    printf("%d\n",(sum-sum1)-sum1);
    return 0;
}

 

来源：CSDN

作者：Zihan_James

链接：https://blog.csdn.net/qq_40639828/article/details/103246716