yxc-dfs

class Solution {
public:
    vector<vector<int>> ans;
    vector<int> res;
    int size=0;

    vector<vector<int>> permutation(vector<int>& nums) {
        size=nums.size();
        res.resize(size);
        sort(nums.begin(), nums.end());
        dfs(nums, 0, 0, 0);
        return ans;
    }

    void dfs(vector<int> &nums, int u, int start, int st)
    {
        if(u==size)
        {
            ans.emplace_back(res);
            return;
        }

        if(!u||nums[u]!=nums[u-1]) start = 0;

        for(int i=start; i<size; ++i)
            if(!(st>>i&1))
            {
                res[i] = nums[u];
                dfs(nums, u+1, i+1, st+(1<<i));
            }
    }
};

next_permutation

class Solution {
public:
    vector<vector<int>> permutation(vector<int>& nums) {
        vector<vector<int>> ans;
        sort(nums.begin(), nums.end());
        do{
            ans.emplace_back(nums);
        }while(next_permutation(nums.begin(), nums.end()));
        return ans;
    }
};

递归（可能超时），AcWing.823题写的，不是乐扣形式

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

int s[10];
vector<vector<int>> ans;
vector<int> res;

void perm(int a[], int l, int r)
{
    if(r==l)
    {
        for(int i=1;i<=r;++i) res.emplace_back(a[i]);
        ans.emplace_back(res);
        res.clear();
    }else
    {
        for(int i=l;i<=r;++i)
        {
            swap(a[l], a[i]);
            perm(a, l+1, r);
            swap(a[l], a[i]);
        }
    }
}

int main()
{
    int n;
    scanf("%d", &n);
    for(int i=0;i<=n;++i) s[i]=i;
    perm(s,1,n);

    sort(ans.begin(), ans.end());

    for(int i=0; i<ans.size(); ++i)
    {
        for(int j=0; j<n; ++j)
        {
            printf("%d ", ans[i][j]);
        }
        puts("");
    }

    return 0;
}