Medium In-place Markers Math & Geometry
In plain English: If any cell in a grid is zero, zero out its entire row and column.
Use the first row and first column as markers. First pass: mark which rows/cols need zeroing. Second pass: zero based on markers. Handle the first row/col separately with a flag.
Prompt
Given an m x n matrix, if an element is 0, set its entire row and column to 0. Do it in-place.
Try to write it from scratch before scrolling down.
Solution
def set_zeroes(matrix):
m, n = len(matrix), len(matrix[0])
first_row_zero = any(matrix[0][j] == 0 for j in range(n))
first_col_zero = any(matrix[i][0] == 0 for i in range(m))
# mark zeros in first row/col
for i in range(1, m):
for j in range(1, n):
if matrix[i][j] == 0:
matrix[i][0] = 0 # mark row
matrix[0][j] = 0 # mark col
# zero cells based on markers
for i in range(1, m):
for j in range(1, n):
if matrix[i][0] == 0 or matrix[0][j] == 0:
matrix[i][j] = 0
# handle first row and col
if first_row_zero:
for j in range(n):
matrix[0][j] = 0
if first_col_zero:
for i in range(m):
matrix[i][0] = 0
return matrix
# Test: set_zeroes([[1,1,1],[1,0,1],[1,1,1]])
# == [[1,0,1],[0,0,0],[1,0,1]]