// 3sum
// Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

// Notice that the solution set must not contain duplicate triplets.
// Example 1:

// Input: nums = [-1,0,1,2,-1,-4]
// Output: [[-1,-1,2],[-1,0,1]]
// Example 2:

// Input: nums = []
// Output: []
// Example 3:

// Input: nums = [0]
// Output: []
//naive approach is o(n^3)
// using three loops 
 