<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:
    vector<int> leftmin(vector<int> arr){
        int n = arr.size();
        stack<int> st;
        vector<int> ans(n,0);
        for(int i = n-1; i>=0; i--){
            while(!st.empty() && arr[st.top()]>arr[i]){
                ans[st.top()]=i;
                st.pop();
            }st.push(i);
        }while(!st.empty()){
            ans[st.top()] = -1;
            st.pop();
        }return ans;
    }
    vector<int> rightmin(vector<int> arr){
        int n = arr.size();
        stack<int> st;
        vector<int> ans(n,0);
        for(int i = 0; i<n; i++){
            while(!st.empty() && arr[st.top()]>arr[i]){
                ans[st.top()]=i;
                st.pop();
            }st.push(i);
        }while(!st.empty()){
            ans[st.top()] = -1;
            st.pop();
        }return ans;
    }
    int findarea(vector<int> arr){
        int n = arr.size();
        vector<int> left = leftmin(arr);
        vector<int> right = rightmin(arr);
        int ans = 0;
        for(int i=0; i<n; i++){
            int l = (left[i]==-1)?0:left[i]+1;
            int r = (right[i]==-1)?n-1:right[i]-1;
            int area = arr[i]*(r-l+1);
            ans = max(ans,area);
        }return ans;
    }
    int maximalRectangle(vector<vector<char>>& matrix) {
        int n = matrix.size();
        int m = matrix[0].size();
        vector<int> height(m,0);
        int ans=0;
        for(int i = 0 ; i<n ; i++){
            for(int j=0;j<m;j++){
                if(matrix[i][j]=='1') height[j]++;
                else height[j]=0;
            }
            int area = findarea(height);
            ans = max(ans,area);
        }return ans;
    }
};
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