思路

• 排序，人为规定顺序去重。
• 深搜+回溯

class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    vector<bool> st;
    int n;
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        n = nums.size();
        st.resize(n);
        path.resize(n);
        sort(nums.begin(), nums.end());
        dfs(nums, 0, 0); //人为规定顺序
        return res;
    }
    void dfs(vector<int>& nums, int u, int start){
        if(u == n){
            res.push_back(path);
            return;
        }
        
        for(int i = start; i < n; i++){
            if(!st[i]){
                st[i] = true;
                path[i] = nums[u]; //i这个位置放哪个数
                dfs(nums, u+1, u+1<n && nums[u+1]==nums[u]? i+1: 0);
                st[i] = false;
            }
        }
    }
};