快速排序&归并排序模板&堆排序

快速排序

void quick_sort(int *a, int l, int r)
{
    if(l >= r) return;
    
    int x = a[(l + r) >> 1];
    int i = l - 1, j = r + 1;

    while(i < j)
    {
        do i++; while(a[i] < x);
        do j--; while(a[j] > x);
        if(i < j) swap(a[i], a[j]);
    }
    quick_sort(a, l, j);
    quick_sort(a, j + 1, r);
}

归并排序

void merge_sort(int *a, int l, int r)
{
    if(l >= r) return;
    
    int mid = (l + r) >> 1;
    merge_sort(a, l, mid);
    merge_sort(a, mid + 1, r);
    
    int i = l, j = mid + 1, k = 1;
    while(i <= mid && j <= r)
    {
        if(a[i] < a[j]) t[k++] = a[i++];
        else t[k++] = a[j++];
    }
    
    while(i <= mid) t[k++] = a[i++];
    while(j <= r) t[k++] = a[j++];
    
    for(int i = l, k = 1; i <= r; i++) a[i] = t[k++];
}

堆排序

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 1e5 + 10;
int a[N], n, len;

void down(int x)
{
	int t = x;
	if (x * 2 <= len && a[t] > a[x * 2])
		t = x * 2;
	if (x * 2 + 1 <= len && a[t] > a[x * 2 + 1])
		t = x * 2 + 1;
	if (t != x)
	{
		swap(a[x], a[t]);
		down(t);
	}
}

int main()
{
	scanf("%d", &n);
	for (int i = 1; i <= n; i++)
	{
		scanf("%d", a + i);
	}
	len = n;

	for (int i = n / 2; i; i--)
	{
		down(i);
	}
	while (n--)
	{
		cout << a[1] << " ";
		a[1] = a[len];
		len--;
		down(1);
	}
	return 0;
}