[LeetCode] 15. 3Sum

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

Note: The solution set must not contain duplicate triplets.

For example, given array S = [-1, 0, 1, 2, -1, -4],

A solution set is:
[
  [-1, 0, 1],
  [-1, -1, 2]
]

 1 class Solution {
 2 public:
 3     vector<vector<int>> threeSum(vector<int>& nums) {
 4         vector<vector<int>> ret;
 5
 6         sort(nums.begin(), nums.end());
 7
 8         for (int i = 0; i < nums.size(); i++){
 9             // if i is  scanced already, skip it
10             if (i > 0 && nums[i] == nums[i-1]) continue;
11             int left = i + 1;
12             int right = nums.size() - 1;
13             while (left < right){
14                 if ((nums[left] + nums[right]) < -nums[i]){
15                     left++;
16                 }else if ((nums[left] + nums[right]) > -nums[i]){
17                     right--;
18                 }else{
19                     vector<int> tmp;
20                     tmp.push_back(nums[i]);
21                     tmp.push_back(nums[left]);
22                     tmp.push_back(nums[right]);
23                     ret.push_back(tmp);
24                     left++;
25                     right--;
26                     // remove duplicates!
27                     while(nums[left] == nums[left - 1]) left++;
28                     while(nums[right] == nums[right+1]) right--;
29                 }
30             }
31         }
32
33         return ret;
34     }
35 };