1329-sort-the-matrix-diagonally.py

"""
Problem Link: https://leetcode.com/problems/sort-the-matrix-diagonally/

A matrix diagonal is a diagonal line of cells starting from some cell in either the topmost row or leftmost column and 
going in the bottom-right direction until reaching the matrix's end. For example, the matrix diagonal starting from mat[2][0], 
where mat is a 6 x 3 matrix, includes cells mat[2][0], mat[3][1], and mat[4][2].
Given an m x n matrix mat of integers, sort each matrix diagonal in ascending order and return the resulting matrix.

Example 1:
Input: mat = [[3,3,1,1],[2,2,1,2],[1,1,1,2]]
Output: [[1,1,1,1],[1,2,2,2],[1,2,3,3]]
 
Constraints:
m == mat.length
n == mat[i].length
1 <= m, n <= 100
1 <= mat[i][j] <= 100
"""
class Solution:
    def diagonalSort(self, mat: List[List[int]]) -> List[List[int]]:
        diagnoals = collections.defaultdict(list)
        
        for i, row in enumerate(mat):
            for j, val in enumerate(row):
                diagnoals[i-j].append(val)
                
        for d in diagnoals.values():
            d.sort(reverse=True)
            
        for i, row in enumerate(mat):
            for j, _ in enumerate(row):
                mat[i][j] = diagnoals[i-j].pop()
                
        return mat