1. 问题描述

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: The solution set must not contain duplicate quadruplets.

For 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]
]

Tags：Array Hash Table Two Pointers

Similar Problems： (E) Two Sum (M) 3Sum

2. 解答思路
3. 代码

4. 反思

原文：http://www.cnblogs.com/whl2012/p/5578845.html