4.1递归和排序

C++

#include <bits/stdc++.h>

using namespace std;
int n;
int a[15], cnt = 0;

void prem(int begin) {
    if (begin == n + 1) {
        cnt++;
        for (int i = 1; i <= n; i++) {
            cout << a[i] << " ";
        }
        cout << endl;
        return;
    }
    for (int i = begin; i <= n; i++) {
        swap(a[begin], a[i]);
        prem(begin + 1);
        swap(a[begin], a[i]);
    }
}

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++)
        a[i] = i;
    prem(1);
    cout << cnt << endl;
    return 0;
}

Python

n = int(input())
arr = [i for i in range(1, n + 1)]


def perm(begin):
    if begin == n:
        for i in arr[:-1]:
            print(i, end=' ')
        print(arr[-1])
        return
    for i in range(begin, n):
        arr[begin], arr[i] = arr[i], arr[begin]
        perm(begin + 1)
        arr[begin], arr[i] = arr[i], arr[begin]


perm(0)