퀵 정렬 실행시간(구현)

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<algorithm>
#define MAX 1000000
using namespace std;
struct POINT
{
    int x;
    int y;
};
int N, S[MAX];
void print_array()
{
    for(int i=0; i<N; i++) printf("%d ", S[i]);
    printf("\n");
}

void swap(int a, int b)
{
    int t = S[a];
    S[a] = S[b];
    S[b] = t;
}

bool compare(POINT a, POINT b)
{
    if(a.x == b.x) return a.y < b.y;
    else return a.x < b.x; // x멤버 기준으로 오름차순
}

void selection_sort(void)
{
    for(int i=0; i<N-1; i++)
    {
        for(int j=i+1; j<N; j++)
        {
            if(S[i] > S[j]) swap(i, j);
        }
    }
}

void quick_sort(int s, int e)
{
    if(s<e)
    {
        int p = s, l = s+1, r = e;
        while(l<=r)
        {
            while(l<=e and S[l]<=S[p]) l++;
            while(r>=s+1 and S[r]>=S[p]) r--;
            if(l<r) swap(l, r);
        }
        swap(p, r);
        quick_sort(s, r-1);
        quick_sort(r+1, e);
    }
}
int main()
{
    srand(time(NULL));
    scanf("%d", &N);
    for(int i=0; i<N; i++) S[i] = rand();
    // print_array();
    int start = clock();

    // selection_sort();
    // sort(S, S+N);
    quick_sort(0, N-1);
    printf("result=%.3lf(sec)\n", (double)(clock()-start)/CLOCKS_PER_SEC);
    // print_array();
}