[Solved] Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

Question

Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

• 0 <= a, b, c, d < n
• a, b, c, and d are distinct.
• nums[a] + nums[b] + nums[c] + nums[d] == target

You may return the answer in any order.

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 = [2,2,2,2,2], target = 8
Output: [[2,2,2,2]]

Constraints:

• 1 <= nums.length <= 200
• -109 <= nums[i] <= 109
• -109 <= target <= 109

Python Solution

class Solution:
    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
        result = []
        nums.sort()

        for i in range(len(nums)):
            t1 = target-nums[i]

            for j in range(i+1,len(nums)):

                #two sum starts form here        
                t2 = t1-nums[j]
                ht = {}
                for k in range(j+1,len(nums)):
                    if nums[k] in ht:
                        if [nums[i],nums[j],nums[k],t2-nums[k]] not in result:
                            result.append([nums[i],nums[j],nums[k],t2-nums[k]])
                    else:
                         ht[t2-nums[k]] = k
        return result