遍历整个矩阵，如果matrix[i][j]==0，那么就记下将行号和列号记下。再遍历一遍矩阵，如果当前行数或列数刚刚被记过，那么就将该数置为0。
class Solution:
def setZeroes(self, matrix: List[List[int]]) -> None:
"""
Do not return anything, modify matrix in-place instead.
"""
if not matrix:
return matrix
l1 = len(matrix)
l2 = len(matrix[0])
row = [0 for _ in range(l1)]
col = [0 for _ in range(l2)]
for i in range(l1):
for j in range(l2):
if matrix[i][j] == 0:
row[i] = 1
col[j] = 1
for i in range(l1):
for j in range(l2):
if row[i] == 1 or col[j] == 1:
matrix[i][j] = 0
return