leetcode 47. Permutations II

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

Example:

Input: [1,1,2]
Output:
[
  [1,1,2],
  [1,2,1],
  [2,1,1]
]

思路

class Solution {
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        int len = nums.size();
        sort(nums.begin(), nums.end());
        vector<int> v;
        vector<vector<int> > res;
        vector<bool> visited(len, false);
        permuteUnique(nums, v, res, visited, 0, len);
        return res;
    }
    //visited用于判断是否访问过， i表示v的长度， len表示nums的长度
    void permuteUnique(vector<int> &nums, vector<int> &v, vector<vector<int> > &res, vector<bool> &visited, int i, int len) {
        if (i == len) {
            res.push_back(v);
            return ;
        }
        for (int k = 0; k < len; k++) {
            if (k > 0 && nums[k] == nums[k - 1] && visited[k - 1]) {
                continue;
            }
            if (visited[k] == false) {
                visited[k] = true;
                v.push_back(nums[k]);
                permuteUnique(nums, v, res, visited, i + 1, len);
                v.pop_back();
                visited[k] = false;
            }
        }
    }

};