[2-4] Chapter Two examples permutation problem

N digital inputs, it outputs all permutations

【answer】

The overall idea is to generate a number of aligned
①-> from the back of the n-1 digits a number picked to replace it on the first position (n-1) th program.
② arranged behind the generation number n-1.
This step is repeated two it
(In Flag feeling than before that [] array method useful method)

[Code]

#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;

const int N = 10;

int n;
int a[N+10];
int cnt = 0;

void dfs(int k,int m){
    if (k==m+1){
        cout<<++cnt<<":";
        for (int i = 1;i <= m;i++){
            cout<<a[i]<<' ';
        }
        cout<<endl;
        return;
    }
    for (int i = k;i <= m;i++){
        swap(a[k],a[i]);
        dfs(k+1,m);
        swap(a[k],a[i]);
    }
}

int main(){
    cin >> n;
    for (int i = 1;i <= n;i++) cin >> a[i];
    dfs(1,n);
    return 0;
}