# ---
# title: 18. 4Sum
# id: problem18
# author: Tian Jun
# date: 2020-10-31
# difficulty: Medium
# categories: Array, Hash Table, Two Pointers
# link: <https://leetcode.com/problems/4sum/description/>
# hidden: true
# ---
# 
# Given an array `nums` of _n_ integers and an integer `target`, are there
# elements _a_ , _b_ , _c_ , and _d_ in `nums` such that _a_ \+ _b_ \+ _c_ \+
# _d_ = `target`? Find all unique quadruplets in the array which gives the sum
# of `target`.
# 
# **Notice**  that the solution set must not contain duplicate quadruplets.
# 
# 
# 
# **Example 1:**
# 
#     
#     
#     Input: nums = [1,0,-1,0,-2,2], target = 0
#     Output: [[-2,-1,1,2],[-2,0,0,2],[-1,0,0,1]]
#     
# 
# **Example 2:**
# 
#     
#     
#     Input: nums = [], target = 0
#     Output: []
#     
# 
# 
# 
# **Constraints:**
# 
#   * `0 <= nums.length <= 200`
#   * `-109 <= nums[i] <= 109`
#   * `-109 <= target <= 109`
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
