leetcode 15 : three sum : python solution

LeetCode problem 15, "3Sum," involves finding all unique triplets in an array that sum to zero. Given an integer array `nums`, the goal is to return all combinations of three numbers such that their sum equals zero, without duplicates. The problem can be solved efficiently using sorting and a two-pointer technique. After sorting the array, we iterate through it and for each number, use two pointers to find the remaining two numbers that make the sum zero. This approach reduces the time complexity to O(n²), making it efficient for medium-sized inputs while ensuring no duplicate triplets are returned.