Leetcode•Nov 05, 2026

Cells with Odd Values in a Matrix

Hazrat Ali

Leetcode

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.

For each location indices[i], do both of the following:

  1. Increment all the cells on row ri.
  2. Increment all the cells on column ci.

Given m, n, and indices, return the number of odd-valued cells in the matrix after applying the increment to all locations in indices.

 

Example 1:

Input: m = 2, n = 3, indices = [[0,1],[1,1]]
Output: 6
Explanation: Initial matrix = [[0,0,0],[0,0,0]].
After applying first increment it becomes [[1,2,1],[0,1,0]].
The final matrix is [[1,3,1],[1,3,1]], which contains 6 odd numbers.

Example 2:

Input: m = 2, n = 2, indices = [[1,1],[0,0]]
Output: 0
Explanation: Final matrix = [[2,2],[2,2]]. There are no odd numbers in the final matrix.

Solution
var oddCells = function(m, n, indices) {
    const rows = new Array(m).fill(0);
    const cols = new Array(n).fill(0);

    for (const [r, c] of indices) {
        rows[r]++;
        cols[c]++;
    }

    let count = 0;

    for (let i = 0; i < m; i++) {
        for (let j = 0; j < n; j++) {
            if ((rows[i] + cols[j]) % 2 !== 0) {
                count++;
            }
        }
    }

    return count;
};
 

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