【leetcode】Permutations II

Permutations II

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

For example,
[1,1,2] have the following unique permutations:
[1,1,2], [1,2,1], and [2,1,1].

 

先排序，如果一个元素与上一个元素相等，且前面没有使用该元素，则该元素不参与当前排列

 

 

 1 class Solution {

 2 public:

 3     vector<vector<int> > permuteUnique(vector<int> &num) {

 4        

 5         sort(num.begin(),num.end());

 6         vector<vector<int> > result;

 7         vector<int> tmp;

 8         vector<bool> visited(num.size());

 9         dfs(0,num,result,visited,tmp);

10         return result;

11        

12     }

13    

14    

15     void dfs(int level,vector<int> &num,vector<vector<int> > &result,vector<bool> &visited,vector<int> &tmp)

16     {

17         if(level==num.size())

18         {

19             result.push_back(tmp);

20             return;

21         }

22        

23         for(int i=0;i<num.size();i++)

24         {

25             if(!visited[i])

26             {

27                 if(i>=1&&((num[i]==num[i-1]&&visited[i-1])||(num[i]!=num[i-1]))||i==0)

28                 {

29                     visited[i]=true;

30                     tmp.push_back(num[i]);

31                     dfs(level+1,num,result,visited,tmp);

32                     tmp.pop_back();

33                     visited[i]=false;

34                 }

35             }

36         }

37     }

38    

39 };