poj2388

快排或者随机快排都超时。

快排：

#include <stdio.h>  
#include <stdlib.h>  
  
int n;  
int d[10005];  
  
int partition(int a[], int p, int r) {  
    double x = a[r];  
    int i = p - 1;  
    int temp;  
    for(int j=p; j<r; j++)  
        if(a[j] <= x) {  
            i++;  
            temp = a[j];  
            a[j] = a[i];  
            a[i] = temp;  
        }  
    temp = a[i+1];  
    a[i+1] = a[r];  
    a[r] = temp;  
    return i + 1;  
}  
  
void quickSort(int a[], int p, int r) {  
    if(p < r) {  
        int q = partition(a, p, r);  
        quickSort(a, p, q-1);  
        quickSort(a, p+1, r);  
    }  
}  
  
int main() {  
      
    while(~scanf("%d", &n)) {  
          
        for(int i=0; i<n; i++)  
            scanf("%d", &d[i]);  
              
        quickSort(d, 0, n-1);  
          
        printf("%d\n", d[(n-1)/2]);  
    }  
      
    return 0;  
}  

随机快排：

#include <stdio.h>
#include <stdlib.h>

int n;
int d[10005];

int partition(int a[], int p, int r) {
	double x = a[r];
	int i = p - 1;
	int temp;
	for(int j=p; j<r; j++)
		if(a[j] <= x) {
			i++;
			temp = a[j];
			a[j] = a[i];
			a[i] = temp;
		}
	temp = a[i+1];
	a[i+1] = a[r];
	a[r] = temp;
	return i + 1;
}

int randomizedPartition(int a[], int p, int r) {
	int i = rand() % (r-p) + p;
	int temp = a[r];
	a[r] = a[i];
	a[i] = temp;
	return partition(a, p, r);
}

void quickSort(int a[], int p, int r) {
	if(p < r) {
		int q = randomizedPartition(a, p, r);
		quickSort(a, p, q-1);
		quickSort(a, p+1, r);
	}
}

int main() {
	
	while(~scanf("%d", &n)) {
		
		for(int i=0; i<n; i++)
			scanf("%d", &d[i]);
			
		quickSort(d, 0, n-1);
		
		printf("%d\n", d[(n-1)/2]);
	}
	
	return 0;
}

sort函数：

#include <iostream>
#include <algorithm>

using namespace std;

int n;
int d[10005];

int main() {
	
	while(cin >> n) {
		
		for(int i=0; i<n; i++)
			cin >> d[i];
			
		sort(d, d+n);
		
		cout << d[(n-1)/2];
	}
	
	return 0;
}