[LeetCode] 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> > ans;    vector<int> v;    bool nums[100];    int len;    vector<vector<int> > permuteUnique(vector<int> &num) {        len = num.size();        memset(nums,false,sizeof(nums));        sort(num.begin(), num.end());        generate(num);        return ans;    }    void generate(vector<int> &num){        if(v.size() == len){            ans.push_back(v);            return;        }        for(int i = 0;i < len;i ++){            if(nums[i] == false){                if(i > 0 && num[i - 1] == num[i] && nums[i - 1] == false)                    continue;                v.push_back(num[i]);                nums[i] = true;                generate(num);                v.pop_back();                nums[i] = false;            }        }    }};