Cells with Odd Values in a Matrix
<p>There is an <code>m x n</code> matrix that is initialized to all <code>0</code>&#39;s. There is also a 2D array <code>indices</code> where each <code>indices[i] = [r<sub>i</sub>, c<sub>i</sub>]</code> represents a <strong>0-indexed location</strong> to perform some increment operations on the matrix.</p>

<p>For each location <code>indices[i]</code>, do <strong>both</strong> of the following:</p>

<ol>
	<li>Increment <strong>all</strong> the cells on row <code>r<sub>i</sub></code>.</li>
	<li>Increment <strong>all</strong> the cells on column <code>c<sub>i</sub></code>.</li>
</ol>

<p>Given <code>m</code>, <code>n</code>, and <code>indices</code>, return <em>the <strong>number of odd-valued cells</strong> in the matrix after applying the increment to all locations in </em><code>indices</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1200-1299/1252.Cells%20with%20Odd%20Values%20in%20a%20Matrix/images/e1.png" style="width: 600px; height: 118px;" />
<pre>
<strong>Input:</strong> m = 2, n = 3, indices = [[0,1],[1,1]]
<strong>Output:</strong> 6
<strong>Explanation:</strong> 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.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1200-1299/1252.Cells%20with%20Odd%20Values%20in%20a%20Matrix/images/e2.png" style="width: 600px; height: 150px;" />
<pre>
<strong>Input:</strong> m = 2, n = 2, indices = [[1,1],[0,0]]
<strong>Output:</strong> 0
<strong>Explanation:</strong> Final matrix = [[2,2],[2,2]]. There are no odd numbers in the final matrix.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= m, n &lt;= 50</code></li>
	<li><code>1 &lt;= indices.length &lt;= 100</code></li>
	<li><code>0 &lt;= r<sub>i</sub> &lt; m</code></li>
	<li><code>0 &lt;= c<sub>i</sub> &lt; n</code></li>
</ul>

<p>&nbsp;</p>
<p><strong>Follow up:</strong> Could you solve this in <code>O(n + m + indices.length)</code> time with only <code>O(n + m)</code> extra space?</p>
Array; Math; Simulation
class Solution {
    public int oddCells(int m, int n, int[][] indices) {
        int[][] g = new int[m][n];
        for (int[] e : indices) {
            int r = e[0], c = e[1];
            for (int i = 0; i < m; ++i) {
                g[i][c]++;
            }
            for (int j = 0; j < n; ++j) {
                g[r][j]++;
            }
        }
        int ans = 0;
        for (int[] row : g) {
            for (int v : row) {
                ans += v % 2;
            }
        }
        return ans;
    }
}