代码随想录：全排列二

class Solution {
public:
    vector<int> path;
    vector<vector<int>> res;
    vector<bool> used;
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        used = vector<bool>(nums.size(), false);
        sort(nums.begin(), nums.end());
        bt(nums);
        return res;
    }

    void bt(vector<int>& nums) {
        if (nums.size() == path.size()) {
            res.push_back(path);
            return;
        }

        for (int i = 0; i < nums.size(); i++) {
            if (used[i] == true)
                continue;
            if (i > 0 && nums[i] == nums[i - 1] && used[i - 1] == true) {
                continue;
            }
            path.push_back(nums[i]);
            used[i] = true;
            bt(nums);
            path.pop_back();
            used[i] = false;
        }
    }
};