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]
]

题解：

set去重

class Solution {
public:
  void dfs(vector<int>& nums, set<vector<int>>& ans, int n, int k, vector<int> tmp, vector<bool>& visit) {
    for (int i = 0; i < n; i++) {
      if (visit[i] == false) {
        tmp.push_back(nums[i]);
        visit[i] = true;
        if (k == n - 1) {
          ans.insert(tmp);
        }
        else {
          dfs(nums, ans, n, k + 1, tmp, visit);
        }
        tmp.pop_back();
        visit[i] = false;
      }
    }
  }
  vector<vector<int>> permuteUnique(vector<int>& nums) {
    sort(nums.begin(), nums.end());
    int n = nums.size();
    set<vector<int>> ans;
    vector<int> tmp;
    vector<bool> visit(n + 1, false);
    dfs(nums, ans, n, 0, tmp, visit);
    vector<vector<int>> res(ans.begin(), ans.end());
    return res;
  }
};

排序后处理：

class Solution {
public:
    void dfs(vector<bool> &visit, vector<int> &tmp, vector<int> &nums, int k, int n, vector<vector<int>> &res) {
        if (k == n) {
            res.push_back(tmp);
        }
        for (int i = 0; i < n; i++) {
            if (i > 0 && nums[i] == nums[i - 1] && visit[i - 1] == false) {
                continue;
            }
            if (visit[i] == false) {
                tmp.push_back(nums[i]);
                visit[i] = true;
                dfs(visit, tmp, nums, k + 1, n, res);
                tmp.pop_back();
                visit[i] = false;
            }
        }
    }
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        int n = nums.size();
        vector<vector<int>> res;
        vector<int> tmp;
        vector<bool> visit(n, false);
        sort(nums.begin(), nums.end());
        dfs(visit, tmp, nums, 0, n, res);
        return res;
    }
};