Given a list of integers nums and an integer target, return all distinct quadruples [a, b, c, d] (values taken from four different indices) with a + b + c + d == target. Each quadruple must be sorted in non-decreasing order; the order of quadruples in the output does not matter.
Examples
Input: nums = [1, 0, -1, 0, -2, 2], target = 0
Output: [[-2, -1, 1, 2], [-2, 0, 0, 2], [-1, 0, 0, 1]]
Input: nums = [2, 2, 2, 2, 2], target = 8
Output: [[2, 2, 2, 2]]
Constraints
0 <= len(nums) <= 300,-10**9 <= nums[i] <= 10**9- Target: O(n^3) time, O(1) extra space beyond the output.
Goals
- Nest two fixed indices around a converging two-pointer scan
- Skip duplicate values at every level so each quadruple is reported once