4Sum

Problem

Given an array S of n integers, are 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.

Example

Given array S = {1 0 -1 0 -2 2}, and target = 0. A solution set is:

(-1, 0, 0, 1)
(-2, -1, 1, 2)
(-2, 0, 0, 2)

Note

Elements in a quadruplet (a,b,c,d) must be in non-descending order. (i.e. a ≤ b ≤ c ≤ d)

The solution set must not contain duplicate quadruplets.

Solution

Very similar to 3Sum, just add another loop.