Four Sum Problem

You are given an array of integers \(nums\) and an integer \(target\). Your task is to find all unique quadruplets \([a, b, c, d]\) in the array such that:

\(a + b + c + d = target\)

Each quadruplet should be listed in non‐decreasing order, and the solution set must not contain duplicate quadruplets. This is a classic problem that can be solved efficiently using sorting and the two‐pointers technique.

Note: Use stdin to receive the input and stdout to print the result.

inputFormat

The input is read from stdin and consists of three lines:

1. An integer \(n\) representing the number of elements in the array.
2. \(n\) space-separated integers representing the array \(nums\).
3. An integer \(target\), the target sum.

For example:

6
1 0 -1 0 -2 2
0

outputFormat

The output should be printed to stdout as a list (in Python list format) of quadruplets. Each quadruplet is represented as a list of four integers in non-decreasing order. If no quadruplets exist, print an empty list [].

For example:

[[-2, -1, 1, 2], [-2, 0, 0, 2], [-1, 0, 0, 1]]

## sample

6
1 0 -1 0 -2 2
0

[[-2, -1, 1, 2], [-2, 0, 0, 2], [-1, 0, 0, 1]]