Cells with Odd Values in a Matrix — LeetCode 1252 Python Solution

The problem

There is an m x n matrix that is initialized to all 0's. There is also a 2D array indices where each indices[i] = [ri, ci] represents a 0-indexed location to perform some increment operations on the matrix.

Example

Input

m = 2, n = 3, indices = [[0,1],[1,1]]

Output

6

Explanation

Initial matrix = [[0,0,0],[0,0,0]].

Python solution

class Solution:
    def oddCells(self, m: int, n: int, indices: List[List[int]]) -> int:
        g = [[0] * n for _ in range(m)]
        for r, c in indices:
            for i in range(m):
                g[i][c] += 1
            for j in range(n):
                g[r][j] += 1
        return sum(v % 2 for row in g for v in row)

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 1252. Cells with Odd Values in a Matrix is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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