LeetCode 47. 全排列 II

首刷自解

思路：回溯+剪枝。需要理解树枝和数层去重

class Solution {
private:
    vector<vector<int>> ret;
    vector<int> path;

    void dfs(vector<int>& nums, vector<bool>& used) {
        if(path.size() == nums.size()){
            ret.push_back(path);
            return;
        }

        for (int i = 0; i < nums.size(); i++) {
            if(used[i] == true) continue;//树枝去重
            if(i > 0 && nums[i] == nums[i-1] && used[i-1]  == false) continue;//数层去重
            used[i] = true;
            path.push_back(nums[i]);

            dfs(nums, used);

            used[i] = false;
            path.pop_back();
        }
    }
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        vector<bool> used(nums.size()+1, false);
        dfs(nums, used);
        return ret;
    }
};