基础算法：快速排序、归并排序

1、快速排序

#include <iostream>
using namespace std;

const int N = 1e5 + 10;
int n, q[N];

void qksort(int q[], int l, int r) {
    if (l >= r) return;

    int x = q[l], i = l - 1, j = r + 1;
    while (i < j) {
        do i++; while (q[i] < x);
        do j--; while (q[j] > x);
        if (i < j) swap(q[i], q[j]);
    }
    
    qksort(q, l, j), qksort(q, j + 1, r);
}

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) scanf("%d", &q[i]);

    qksort(q, 0, n - 1);
    
    for (int i = 0; i < n; i++) printf("%d ", q[i]);

    return 0;
}

2、归并排序

#include <iostream>
using namespace std;

const int N = 1e5 + 10;
int n, q[N], tmp[N];

void mergeSort(int q[], int l, int r) {
    if (l >= r) return;
    
    int mid = (l + r) >> 1;
    mergeSort(q, l, mid), mergeSort(q, mid + 1, r);
    
    int k = 0, i = l, j = mid + 1;
    while (i <= mid && j <= r) {
        if (q[i] <= q[j]) tmp[k++] = q[i++];
        else tmp[k++] = q[j++];
    }
    while (i <= mid) tmp[k++] = q[i++];
    while (j <= r) tmp[k++] = q[j++];

    for (i = l, j = 0; i <= r; i++, j++) q[i] = tmp[j];
}

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) scanf("%d", &q[i]);
    
    mergeSort(q, 0, n - 1);
    
    for (int i = 0; i < n; i++) printf("%d ", q[i]);

    return 0;
}