LeetCode解题报告：498. Diagonal Traverse

Problem

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.

解题思路

  这一题不难，但是很麻烦，一不小心就容易出错。代码如下：

class Solution:
    def findDiagonalOrder(self, matrix: list) -> list:
        if not matrix:
            return []
        row = len(matrix)
        col = len(matrix[0])

        ans = []
        flag = 0
        for s in range(row + col - 2 + 1):
            line = []
            l = max(0, s - col + 1)
            r = min(row - 1, s)
            for i in range(l, r + 1):
                line.append(matrix[i][s - i])
            if flag:
                ans += line
            else:
                ans += line[::-1]
            flag = 1 - flag
        return ans