Java for Leetcode 018 4Sum

Given an array S of n integers, is there elements a, b, C, and D in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Problem Solving Ideas:

The first is definitely a sort, and if it's a brute-force enumeration, it's definitely timed out. Therefore, we can use the idea of divided treatment, storage of all 2 elements of the and, and then use the idea of 2SUM to solve, so the time complexity of O (n^2)

The Java implementation is as follows:

Java for Leetcode 018 4Sum