0073-set-matrix-zeroes

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Description

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

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?

Solution(Python)

class Solution:
    def setZeroes(self, matrix: List[List[int]]) -> None:
        """
        Do not return anything, modify matrix in-place instead.
        """
        #  collect rows and columns to be filled with zero
        # rows = []
        # cols = []
        # irtate the cells and if zero add row add cols
        # fill rows and cols with zeroes
        #
    
        def hashset():
            m,n = len(matrix), len(matrix[0])
            rows,cols = [], []
            for i in range(m):
                for j in range(n):
                    if matrix[i][j] == 0:
                        rows.append(i)
                        cols.append(j)
            
            for row in rows:
                for j in range(n):
                    matrix[row][j] = 0
            for col in cols:
                for i in range(m):
                    matrix[i][col] = 0

        m, n = len(matrix), len(matrix[0])
        first_row_zero = False
        first_col_zero = False
        
        # Step 1: Check if first row or first column has any zeros
        for j in range(n):
            if matrix[0][j] == 0:
                first_row_zero = True
                break
                
        for i in range(m):
            if matrix[i][0] == 0:
                first_col_zero = True
                break
        
        # Step 2: Use first row and column as markers
        for i in range(1, m):
            for j in range(1, n):
                if matrix[i][j] == 0:
                    matrix[i][0] = 0
                    matrix[0][j] = 0
        
        # Step 3: Zero out 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
        
        # Step 4: Zero out first row and column if needed
        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

Dry Run