4Sum

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

SOLUTION:

class Solution:
    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
        n = len(nums)
        nums.sort()
        res = set()
        for i in range(n):
            a = nums[i]
            for j in range(i + 1, n - 2):
                b = nums[j]
                start = j + 1
                end = n - 1
                while start < end:
                    c = nums[start]
                    d = nums[end]
                    total = b + c + d
                    if total == target - a:
                        res.add(tuple([a, b, c, d]))
                        start += 1
                        end -= 1
                    elif total > target - a:
                        end -= 1
                    else:
                        start += 1
        return list(res)