class Solution:
    def findDiagonalOrder(self, matrix: List[List[int]]) -> List[int]:
        """
        0: [0, 0]
        1: [0, 1] [1, 0]
        2: [2, 0] [1, 1] [0, 2]
        3: [1, 2] [2, 1]
        4: [2, 2]
        """

        m, n = len(matrix), len(matrix[0])

        hashmap = defaultdict(list)
        result = []

        for i in range(m):
            for j in range(n):
                hashmap[(i+j)].append(matrix[i][j])

        for i in range(m-1 + n-1 + 1):
            if i%2 == 0:
                result.extend(hashmap[i][::-1])
            else:
                result.extend(hashmap[i])

        return result