<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>

class Solution {
 public:
  int maxEqualRowsAfterFlips(vector<vector<int>>& matrix) {
    const int m = matrix.size();
    const int n = matrix[0].size();
    int ans = 0;
    vector<int> flip(n);
    unordered_set<int> seen;

    for (int i = 0; i < m; ++i) {
      if (seen.contains(i))
        continue;
      int count = 0;
      for (int j = 0; j < n; ++j)
        flip[j] = 1 ^ matrix[i][j];
      for (int k = 0; k < m; ++k)
        if (matrix[k] == matrix[i] || matrix[k] == flip) {
          seen.insert(k);
          ++count;
        }
      ans = max(ans, count);
    }

    return ans;
  }
};
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