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].

class Solution {
public:
    vector<vector<int> > permuteUnique(vector<int> &num) {
        vector<vector<int>> all;
        map<int,bool> visited;//记录以num[i]开头的组合是否已经计算过
        for(size_t i=0;i<num.size();++i){
            if(visited[num[i]]) continue;
            visited[num[i]]=true;
            vector<int> restCopy(num.begin(),num.end());
            restCopy.erase(restCopy.begin()+i);
            vector<vector<int>> rest = permuteUnique(restCopy);
            if(rest.size()){
                for(size_t j=0;j<rest.size();++j){
                    vector<int> &each = rest[j];
                    each.insert(each.begin(),num[i]);
                    all.push_back(each);
                }
            }else{
                all.push_back(num);
            }
        }
        return all;
    }
};