数字排列

class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    bool st[10];
    void dfs(vector<int>& nums,int u)
    {
        int n=nums.size();
        if(u==n)
        {
            res.push_back(path);
            return;
        }
        set<int> s;
        for (int i = 0; i < n; i ++ )
        {
            if(st[i])   continue;
            if(s.count(nums[i]))   continue;
            s.insert(nums[i]);
            st[i]=true;
            path.push_back(nums[i]);
            dfs(nums,u+1);
            path.pop_back();
            st[i]=false;
        }
    }
    vector<vector<int>> permutation(vector<int>& nums) {
        dfs(nums,0);
        return res;
    }
};