<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 helper(vector<int> & heights){
        int n = heights.size();
        stack<int> st;
        int maxArea=0;
        for(int i=0; i<n; i++){
            while(!st.empty() && heights[st.top()] >= heights[i]){
                int element = heights[st.top()];
                st.pop();
                int nse = i;
                int pse = (st.empty()) ? -1 : st.top();
                int mini = min(element,nse-pse-1);

                maxArea = max(maxArea, mini*mini);
            }
            st.push(i);
        }

        while(!st.empty()){
            int ele = heights[st.top()];
            st.pop();
            int nse = n;
            int pse = (st.empty()) ? -1 : st.top();
            int mini = min(ele,nse-pse-1);

            maxArea = max(maxArea, mini*mini);
        }

        return maxArea;
    }



    int maximalSquare(vector<vector<char>>& matrix) {
         int n = matrix.size();
        int m = matrix[0].size();
        vector<vector<int>> mat(n, vector<int> (m,0));
        for(int j=0; j<m; j++){
            int sum=0;
            for(int i=0; i<n; i++){
                if(matrix[i][j]=='1'){
                    sum+=(matrix[i][j]-48);
                }
                else{
                    sum=0;
                }
                mat[i][j]=sum;
                // cout<<i<<" "<<j<<" "<<sum<<endl;
            }
        }

        int maxArea=0;
        for(int i=0; i<n; i++){
            maxArea = max(maxArea, helper(mat[i]));
        }
        return maxArea;

    }
};
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