<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 help(vector<int>v){

        int ans=0;
        stack<int>st;
        int n=v.size();
        for(int i=0;i<=v.size();i++){
           if(st.empty())
           st.push(i);
           else if(i!=n&&v[i]>v[st.top()]){
            st.push(i);
           }
           else{
            while(!st.empty()&&(i==n||v[st.top()]>=v[i])){
                int h=v[st.top()];
                st.pop();
                int w;
                if(st.empty())
                w=i;
                else
                w=i-st.top()-1;
                ans=max(ans,h*w);//
            }
            st.push(i);
           }
        }
       
        return ans;
    }
    int maximalRectangle(vector<vector<char>>& matrix) {
        int n=matrix.size();
        int m=matrix[0].size();
        vector<vector<int>>mat(n,vector<int>(m,0));


        for(int i=0;i<matrix.size();i++){
            for(int j=0;j<matrix[0].size();j++){
                if(matrix[i][j]=='1')
                mat[i][j]=1;
              
            }
        }
         for(int i=1;i<mat.size();i++){
            for(int j=0;j<mat[0].size();j++){
                if(mat[i][j]==1)
                mat[i][j]=1+mat[i-1][j];
              
            }
        }
        int ans=0;
        for(int i=0;i<matrix.size();i++){
            ans=max(ans,help(mat[i]));
        }
        return ans;
    }
};
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