LeetCode 45. Permutations II

做LeetCode 44. Permutations时，考虑的就是找出所有unique permutations，而且44中也没有考察duplicate的sample, 所以同一份代码都能AC

思路是num排升序，将其加入返回值ret中，再迭代去找它的LeetCode 30. Next Permutation

代码：

class Solution {public:    vector<vector<int> > permute(vector<int> &num)     {vector<vector<int> > ret;sort(num.begin(), num.end());do {ret.push_back( num );} while( has_next_permutation(num) );return ret;}private:bool has_next_permutation(vector<int>& num){for (int i = num.size()-2; i >= 0; -- i){for (int j = num.size()-1; j > i; -- j){if (num[j] > num[i]){swap(num[i], num[j]);sort(num.begin()+i+1, num.end());return true;}}}return false;}};