Given an array nums of n integers, are there elements a, b, c in nums 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.

Example:

Given array nums = [-1, 0, 1, 2, -1, -4],

A solution set is:

[ [-1, 0, 1], [-1, -1, 2] ]

Explaination

For time optimization, we need to sort the given array. Then enumerate the elements from index 0(assume value v0), try to find the 2 elements which some sum of them is -v0.

if(nums.size() < 3) return ans; for(int i=0; i < nums.size(); i++) { int l = i+1, r = nums.size() - 1; int v = -nums[i]; while(l < r) { int s = nums[l] + nums[r]; if (s == v) { vector<int> e {nums[i], nums[l], nums[r]}; ans.push_back(e); l++, r--;

//skip same elements while(l < r && nums[l] == nums[l-1]) l++; while(l < r && nums[r+1] == nums[r]) r--; } elseif(s > v) r--; else l++; } while(i+1 < nums.size() && nums[i+1] == nums[i]) i++; } return ans; } };