015. 3Sum

 1 class Solution {
 2 public:
 3     vector<vector<int>> threeSum(vector<int>& nums) {
 4         vector<vector<int>> result;
 5     //set<vector<int>> temp;
 6         if (nums.size() < 3) return result;
 7         else {
 8             sort(nums.begin(), nums.end());
 9             for (int i = 0; i < nums.size() - 2; ++i) {
10                 if (i != 0 && nums[i] == nums[i - 1]) continue;
11                 int j = i + 1, k = nums.size() - 1;
12                 while (i < j && j < k) {
13                     if (nums[i] + nums[j] + nums[k] == 0) {
14                         result.push_back(vector<int>{nums[i], nums[j], nums[k]});
15                         ++j; --k;
16                         while (nums[j] == nums[j - 1] && j < k) ++j;
17                         while (nums[k] == nums[k + 1] && j < k) --k;
18                     }
19                     else if (nums[i] + nums[j] + nums[k] > 0) {
20                         --k;
21                         while (nums[k] == nums[k + 1] && j < k) --k;
22                     }
23                     else {
24                         ++j;
25                         while (nums[j] == nums[j - 1] && j < k) ++j;
26                     }
27                 }
28             }
29             //result = vector<vector<int>>(temp.begin(), temp.end());
30             return result;
31         }
32     }
33 };