<p>Given a <code>rows x cols</code>&nbsp;binary <code>matrix</code> filled with <code>0</code>&#39;s and <code>1</code>&#39;s, find the largest rectangle containing only <code>1</code>&#39;s and return <em>its area</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/09/14/maximal.jpg" style="width: 402px; height: 322px;" />
<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> 6
<strong>Explanation:</strong> The maximal rectangle is shown in the above picture.
</pre>

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

<pre>
<strong>Input:</strong> matrix = [[&quot;0&quot;]]
<strong>Output:</strong> 0
</pre>

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

<pre>
<strong>Input:</strong> matrix = [[&quot;1&quot;]]
<strong>Output:</strong> 1
</pre>

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

<ul>
	<li><code>rows == matrix.length</code></li>
	<li><code>cols == matrix[i].length</code></li>
	<li><code>1 &lt;= row, cols &lt;= 200</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 largestRectangleArea(vector<int>& h) {
        stack<int> st;
        int ans = 0;
        int n=h.size();
        for(int i=0;i<n;i++){
            if(st.empty() || h[st.top()]<=h[i])
            st.push(i);
            else{
                int tp=0;
                while(!st.empty() && h[st.top()]>h[i])
                {
                    ans=max(ans,h[st.top()]*(i-st.top()));
                    tp=st.top();
                    st.pop();
                }
                st.push(tp);
                h[tp]=h[i];
            }
        }
        while(!st.empty())
                {
                    if(st.size()==1){
                        ans=max(ans, h[st.top()]*n);
                    }
                    else
                    ans=max(ans,h[st.top()]*(n-st.top()));
                    st.pop();
                }

        return ans;
    }
    int maximalRectangle(vector<vector<char>>& matrix) {
        int n=matrix.size(), m=matrix[0].size();
        vector<vector<int> > h(n, vector<int>(m));
        for(int j=0;j<m;j++)
        h[0][j]=matrix[0][j]-'0';
        for(int i=1;i<n;i++){
            for(int j=0;j<m;j++){
                if(matrix[i][j]-'0')
                h[i][j]=h[i-1][j]+1;
                // cout<<h[i][j]<<" ";
            }
            // cout<<endl;
        }
        int ans=0;
        for(int i=0;i<n;i++){
            ans=max(ans, largestRectangleArea(h[i]));
        }
        return ans;
    }
};
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