Leetcode 498. Diagonal Traverse

Seawolf

Given a matrix of M x N elements (M rows, N columns), return all elements of the matrix in diagonal order as shown in the below image.

 

Example:

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

Output:  [1,2,4,7,5,3,6,8,9]

Explanation:

 







Note:

The total number of elements of the given matrix will not exceed 10,000.

class Solution:
    def findDiagonalOrder(self, matrix: List[List[int]]) -> List[int]:
        result = []
        if matrix == None or len(matrix) == 0 or len(matrix[0]) == 0:
            return result
        m = len(matrix)
        n = len(matrix[0])
        hashmap = collections.defaultdict(list)
        for i in range(m):
            for j in range(n):
                hashmap[i + j].append(matrix[i][j])
        for k in sorted(hashmap.keys()):
            temp = hashmap[k]
            if k % 2 == 0:
                temp = temp[::-1]
            result += temp
        return result