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FleetCode

3446. Sort Matrix by Diagonals

Medium84.1% acceptance5 companies

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
  • -105 <= grid[i][j] <= 105

Hints open one at a time

Hint 1
Use a data structure to store all values in each diagonal.
Hint 2
Sort and replace them in the matrix.
38:17
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1class Solution:
2 def sortMatrix(self, grid: List[List[int]]) -> List[List[int]]:
3
Starter codePython 3Spaces: 4
Examples
Input
[[1,7,3],[9,8,2],[4,5,6]]
Input
[[0,1],[1,2]]
Input
[[1]]
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