【LeetCode】4Sum

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.

Note:

Elements in a quadruplet (a,b,c,d)

must be in non-descending order.

(ie, a ≤ b ≤ c ≤ d)

The solution set must not contain duplicate quadruplets.