【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

 

 

class Solution {
public:
    vector<vector<int> > permuteUnique(vector<int> &num) {
       
        sort(num.begin(),num.end());
        vector<vector<int> > result;
        vector<int> tmp;
        vector<bool> visited(num.size());
        dfs(0,num,result,visited,tmp);
        return result;
       
    }
   
   
    void dfs(int level,vector<int> &num,vector<vector<int> > &result,vector<bool> &visited,vector<int> &tmp)
    {
        if(level==num.size())
        {
            result.push_back(tmp);
            return;
        }
       
        for(int i=0;i<num.size();i++)
        {
            if(!visited[i])
            {
                if(i>=1&&((num[i]==num[i-1]&&visited[i-1])||(num[i]!=num[i-1]))||i==0)
                {
                    visited[i]=true;
                    tmp.push_back(num[i]);
                    dfs(level+1,num,result,visited,tmp);
                    tmp.pop_back();
                    visited[i]=false;
                }
            }
        }
    }
   
};