3446 - Sort Matrix by Diagonals.

Medium

You are given an n x n square matrix of integers grid. Return the matrix such that:

• The diagonals in the bottom-left triangle (including the middle diagonal) are sorted in non-increasing order.

• The diagonals in the top-right triangle are sorted in non-decreasing order.

Example 1:

Input: grid = [1,7,3,9,8,2,4,5,6]

Output: [8,2,3,9,6,7,4,5,1]

Explanation:

The diagonals with a black arrow (bottom-left triangle) should be sorted in non-increasing order:

• [1, 8, 6] becomes [8, 6, 1].

• [9, 5] and [4] remain unchanged.

The diagonals with a blue arrow (top-right triangle) should be sorted in non-decreasing order:

• [7, 2] becomes [2, 7].

• [3] remains unchanged.

Example 2:

Input: grid = [0,1,1,2]

Output: [2,1,1,0]

Explanation:

The diagonals with a black arrow must be non-increasing, so [0, 2] is changed to [2, 0]. The other diagonals are already in the correct order.

Example 3:

Input: grid = [1]

Output: [1]

Explanation:

Diagonals with exactly one element are already in order, so no changes are needed.

Constraints:

• grid.length == grid[i].length == n

• 1 <= n <= 10

• <code>-10⁵<= gridj<= 10⁵</code>