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]. Problem link Solution

  • recursive solution, only when last element is not  (the same and used)
class Solution {
    vector<vector > permuteUnique(vector &num) {
        sort(num.begin(), num.end());
        vector<vector> vv;
        vector v;
        vector u(num.size(), false);
        rec(vv, v, u, num);
        return vv;
    void rec(vector<vector> &vv, vector &v, vector &u, vector &num){
        for (int i=0; i<num.size(); ++i){
            if (!u[i] && (i==0 || i>0 && !(num[i]==num[i-1] && !u[i-1]))){
                u[i] = true;
                if (v.size()==num.size()){
                    rec(vv, v, u, num);
                u[i] = false;
Permutations II

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