<p>Given an <code>m x n</code> binary <code>matrix</code> filled with <code>0</code>&#39;s and <code>1</code>&#39;s, <em>find the largest square containing only</em> <code>1</code>&#39;s <em>and return its area</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/26/max1grid.jpg" style="width: 400px; height: 319px;" />
<pre>
<strong>Input:</strong> matrix = [[&quot;1&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;],[&quot;1&quot;,&quot;0&quot;,&quot;1&quot;,&quot;1&quot;,&quot;1&quot;],[&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;1&quot;],[&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;]]
<strong>Output:</strong> 4
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/11/26/max2grid.jpg" style="width: 165px; height: 165px;" />
<pre>
<strong>Input:</strong> matrix = [[&quot;0&quot;,&quot;1&quot;],[&quot;1&quot;,&quot;0&quot;]]
<strong>Output:</strong> 1
</pre>

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

<pre>
<strong>Input:</strong> matrix = [[&quot;0&quot;]]
<strong>Output:</strong> 0
</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 <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
</ul>

class Solution {
public:
    int maximalSquare(vector<vector<char>>& matrix) {
        int row = matrix.size();
        int col = matrix[0].size();
        bool formed = false;
        int ret = 0;
        int i, j;
        for (i = 0; i < row; i ++)
        {
            for (j = 0; j < col; j ++)
                if (matrix[i][j] == '1')
                     break;
            if (j != col)
                break;
        }
        if (i == row)
            return 0;
        
        while (true)
        {
            formed = false;
            for (int i = 1; i < row; i ++)
            {
                for (int j = 1; j < col; j ++)
                {
                    if (matrix[i-1][j-1]=='1'&& matrix[i-1][j]== '1'&& matrix[i][j-1]=='1'&&matrix[i][j]=='1')
                    {
                        matrix[i-1][j-1] = '1';
                        formed = true;
                    }
                    else
                    {
                        matrix[i-1][j-1] = '0';
                    }
                }
            }
            std::cout << "formed:" << formed << std::endl; 
            if (!formed)
            {
                break;
            }
            row --;
            col --;
        }
        return (matrix.size() - row + 1) * (matrix.size() - row + 1);
    }
};
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