This post is part of the Algorithms Problem Solving series.

## Problem description

This is the Odd in Matrix problem. The description looks like this:

Given `n`

and `m`

which are the dimensions of a matrix initialized by zeros and given an array `indices`

where `indices[i] = [ri, ci]`

. For each pair of `[ri, ci]`

you have to increment all cells in row `ri`

and column `ci`

by 1.

Return *the number of cells with odd values* in the matrix after applying the increment to all `indices`

.

## Examples

```
Input: n = 2, m = 3, indices = [[0,1],[1,1]]
Output: 6
Input: n = 2, m = 2, indices = [[1,1],[0,0]]
Output: 0
```

## Solution

- Initialize the matrix with all elements as zero
- For each pair of indices, increment for the row, and increment for the column
- Traverse the matrix counting all the odd numbers
- Return the counter

```
def init_matrix(rows, columns):
return [[0 for _ in range(columns)] for _ in range(rows)]
def odd_cells(n, m, indices):
matrix = init_matrix(n, m)
for [ri, ci] in indices:
for column in range(m):
matrix[ri][column] += 1
for row in range(n):
matrix[row][ci] += 1
odds = 0
for row in range(n):
for column in range(m):
if matrix[row][column] % 2 != 0:
odds += 1
return odds
```

## Top comments (3)

Don't you think there can be a better approach to this problem?

"Better" is a subjective concept. Some could call better this approach:

You can say it's better because it's shorter and faster. But it's much harder to read. If I am asked to maintain it, I would prefer much more TK's approach.

Or something like this:

A lot more code, but way easier to read and understand, in my opinion.

Therefore, I ask you the same: don't you think there can be a better approach to this problem? How would you solve it?

I believe that there is a solution use only 4 numbers: number of columns (rows) which have even (odd) cells on each. Need time to test it...