<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 n = matrix.size(), m = matrix[0].size();
        vector<vector<int>> hor(n,vector<int>(m,0)), dp(n,vector<int>(m,0));
        for(int i = 0;i<n;i++)
        {
            int cnt = 0;
            for(int j = 0;j<m;j++)
            {
                if(matrix[i][j]=='1')
                cnt++;
                else
                cnt = 0;
                hor[i][j] = cnt;
            }
        }
        for(int i = 0;i<m;i++)
        {
            int cnt = 0;
            for(int j = 0;j<n;j++)
            {
                if(matrix[j][i]=='1')
                cnt++;
                else
                cnt = 0;
                hor[j][i] = min(hor[j][i],cnt);
            }
        }
        int ans = 0;
        for(int i = 0;i<n;i++)
        {
            for(int j = 0;j<m;j++)
            {
                if(hor[i][j])
                dp[i][j] = 1;
                if(i>0 && j>0 && dp[i][j])
                {
                    int anss = hor[i][j]-1;
                    anss = min(anss,dp[i-1][j-1]);
                    dp[i][j] = anss+1;
                }
                ans = max(ans,dp[i][j]);
            }
        }
        return ans*ans;
    }
};
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