算法1

dfs+遍历 超时了

#include<bits/stdc++.h>

using namespace std;
#define N 10010

bool st[N];
int a[N];
vector<int> res;
int n;
void dfs(int u)
{
    if(u==n+1)
    {
        int temp = 0;
        for(int i = 1; i <= n;i++)
        {

            temp = temp*10 + a[i];
        }
        res.push_back(temp);
        // cout << temp << endl;

        return;
    }

    for(int i =1;i <=n;i++)
    {
        if( st[i] !=1)
        {
            st[i] = 1;      
            a[u] = i;
            dfs(u+1);
            st[i] = 0;
        }
    }

}

void printfNum(int num)
{
    string str;
    while(num)
    {
        int t = num % 10;
        str += (t + '0');
        num /= 10;    
    }
    reverse(str.begin(),str.end());

    for(int i = 0; i < str.size();i++)
        cout << str[i] << " ";

}

int main()
{
    cin >> n;
    dfs(1);
    int add_num = 0;
    cin >> add_num;

    int cur_index = 0;
    int cur_date = 0;
    for(int i = 1; i <= n;i++)
    {
        int t;
        scanf("%d",&t);
        cur_date = cur_date*10 + t;
    }
    // cout << cur_date;

    for(int i = 0; i < res.size(); i++)
    {
        if( cur_date == res[i])
            cur_index = i; 
    }
    printfNum(res[cur_index+add_num]);
    // cout << res[cur_index+add_num] << endl;
    return 0;
}

算法2

(next_permutation) $O(n)$

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 10010;

int n, m;
int w[N];

int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i ++ ) cin >> w[i];
    while (m -- )
    {
        next_permutation(w , w + n );
    }
    for (int i = 0; i < n; i ++ ) cout << w[i] << ' ';
    cout << endl;

    return 0;
}