Set Matrix Zeroes

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0's, and return the matrix.

You must do it in place.

 

Example 1:

Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]
Output: [[1,0,1],[0,0,0],[1,0,1]]

Example 2:

Input: matrix = [[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]]

 

Constraints:

• m == matrix.length
• n == matrix[0].length
• 1 <= m, n <= 200
• -231 <= matrix[i][j] <= 231 - 1

 

Follow up:

• A straightforward 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?

Solutions:

For to solve it in O(mn), use a copy of given matrix and go through every element of original matrix and update the copy matrix's row and column to zero if a zero if found in original matrix.

Space O(m + n) Solution:

class Solution:
    def setZeroes(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        ROWS, COLS = len(matrix), len(matrix[0])
        rows = [0] * ROWS
        cols = [0] * COLS
        for r in range(ROWS):
            for c in range(COLS):
                if matrix[r][c] == 0:
                    rows[r] = 1
                    cols[c] = 1
        for c in range(COLS):
            for R in range(len(rows)):
                if rows[R] == 1:
                    matrix[R][c] = 0
        for r in range(ROWS):
            for C in range(len(cols)):
                if cols[C] == 1:
                    matrix[r][C] = 0

Space O(1) Solution:

class Solution:
    def setZeroes(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        ROWS, COLS = len(matrix), len(matrix[0])
   
        rowZero = False
        
        for r in range(ROWS):
            for c in range(COLS):
                if matrix[r][c] == 0:
                    matrix[0][c] = 0
                    if r > 0:
                        matrix[r][0] = 0
                    else:
                        rowZero = True
        for r in range(1, ROWS):
            for c in range(1, COLS):
                if matrix[0][c] == 0 or matrix[r][0] == 0:
                    matrix[r][c] = 0
        if matrix[0][0] == 0:
            for r in range(ROWS):
                matrix[r][0] = 0
        if rowZero:
            for c in range(COLS):
                matrix[0][c] = 0