# LeetCode 73. Set Matrix Zeroes

## Description

https://leetcode.com/problems/set-matrix-zeroes/

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in-place.

Example 1:

```Input:
[
[1,1,1],
[1,0,1],
[1,1,1]
]
Output:
[
[1,0,1],
[0,0,0],
[1,0,1]
]
```

Example 2:

```Input:
[
[0,1,2,0],
[3,4,5,2],
[1,3,1,5]
]
Output:
[
[0,0,0,0],
[0,4,5,0],
[0,3,1,0]
]
```

Follow up:

• A straight forward solution using O(mn) space is probably a bad idea.
• A simple improvement uses O(m + n) space, but still not the best solution.
• Could you devise a constant space solution?

## Explanation

If any cell of the matrix has a zero we can record its row and column number.

## Python Solution

``````class Solution:
def setZeroes(self, matrix: List[List[int]]) -> None:
"""
Do not return anything, modify matrix in-place instead.
"""

zero_rows = set()
zero_columns = set()

for i in range(0, len(matrix)):
for j in range(0, len(matrix)):
if matrix[i][j] == 0:
zero_rows.add(i)
zero_columns.add(j)

for i in range(0, len(matrix)):
for j in range(0, len(matrix)):
if i in zero_rows or j in zero_columns:
matrix[i][j] = 0
``````
• Time complexity: O(MN).
• Space complexity: O(M + N).