用visited数组标记要输出即可，当dfs到达边界，遍历数组输出即可

#include <iostream>

using namespace std;

int visited[20] = {0};
int arr[20];
    int n;
void dfs(int nums, int begin, int cur_nums)
{
    if (cur_nums==nums)
    {
        for(int i = 1; i<=n;i++)
        {
            if(visited[i] == 1)
                cout << i <<" ";
        }
        cout << endl;
        return;

    }
    for(int i = begin;i<=n;i++)
    {
        if(visited[i] == 0)
        {
            visited[i] = 1;
            dfs(nums, i+1, cur_nums+1); // 不要用i++和cur_nums++
            visited[i] = 0;

        }
    }
}


int main(){
    cout <<endl;

    cin >>n;

    for(int i=1;i<=n;i++)
        dfs(i, 1, 0);
}