Flip Columns For Maximum Number of Equal Rows
<p>You are given an <code>m x n</code> binary matrix <code>matrix</code>.</p>

<p>You can choose any number of columns in the matrix and flip every cell in that column (i.e., Change the value of the cell from <code>0</code> to <code>1</code> or vice versa).</p>

<p>Return <em>the maximum number of rows that have all values equal after some number of flips</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> matrix = [[0,1],[1,1]]
<strong>Output:</strong> 1
<strong>Explanation:</strong> After flipping no values, 1 row has all values equal.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> matrix = [[0,1],[1,0]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> After flipping values in the first column, both rows have equal values.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> matrix = [[0,0,0],[0,0,1],[1,1,0]]
<strong>Output:</strong> 2
<strong>Explanation:</strong> After flipping values in the first two columns, the last two rows have equal values.
</pre>

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

<ul>
	<li><code>m == matrix.length</code></li>
	<li><code>n == matrix[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 300</code></li>
	<li><code>matrix[i][j]</code> is either&nbsp;<code>0</code> or <code>1</code>.</li>
</ul>
Array; Hash Table; Matrix
class Solution {
public:
    int maxEqualRowsAfterFlips(vector<vector<int>>& matrix) {
        unordered_map<string, int> cnt;
        int ans = 0;
        for (auto& row : matrix) {
            string s;
            for (int x : row) {
                s.push_back('0' + (row[0] == 0 ? x : x ^ 1));
            }
            ans = max(ans, ++cnt[s]);
        }
        return ans;
    }
};