3033. Modify the Matrix

Problem Link

Description

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Given a 0-indexed m x n integer matrix matrix, create a new 0-indexed matrix called answer. Make answer equal to matrix, then replace each element with the value -1 with the maximum element in its respective column.

Return the matrix answer.

 

Example 1:

Input: matrix = [[1,2,-1],[4,-1,6],[7,8,9]]
Output: [[1,2,9],[4,8,6],[7,8,9]]
Explanation: The diagram above shows the elements that are changed (in blue).
- We replace the value in the cell [1][1] with the maximum value in the column 1, that is 8.
- We replace the value in the cell [0][2] with the maximum value in the column 2, that is 9.

Example 2:

Input: matrix = [[3,-1],[5,2]]
Output: [[3,2],[5,2]]
Explanation: The diagram above shows the elements that are changed (in blue).

 

Constraints:

• m == matrix.length
• n == matrix[i].length
• 2 <= m, n <= 50
• -1 <= matrix[i][j] <= 100
• The input is generated such that each column contains at least one non-negative integer.

Solution

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Python3

class Solution:
    def modifiedMatrix(self, matrix: List[List[int]]) -> List[List[int]]:
        rows, cols = len(matrix), len(matrix[0])
        colMax = [0] * cols
        
        for j, col in enumerate(zip(*matrix)):
            colMax[j] = max(col)
        
        for i in range(rows):
            for j in range(cols):
                if matrix[i][j] == -1:
                    matrix[i][j] = colMax[j]
        
        return matrix