1424. Diagonal Traverse II

https://leetcode.com/problems/diagonal-traverse-ii

Python

from collections import defaultdict


class Solution:
    def findDiagonalOrder(self, nums: List[List[int]]) -> List[int]:
        mapper = defaultdict(list)

        for i in range(len(nums)-1, -1, -1):
            for j in range(len(nums[i])):
                mapper[i+j].append(nums[i][j])

        result = []
        for key in sorted(mapper.keys()):
            result += mapper[key]

        return result