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