int largestRectangleArea(vector<int>& heights) {
        stack<int> s;
        heights.push_back(0);
        int result=0;
        for(int i=0;i<heights.size();)
        {
            if(s.empty()||heights[i]>heights[s.top()])
            {
                s.push(i++);
            }
            else
            {
                int tmp=s.top();
                s.pop();
                result=max(result,heights[tmp]*(s.empty()?i:i-s.top()-1));
            }
        }
        return result;
    }
    int maximalRectangle(vector<vector<char>>& matrix) {
        int m=matrix.size();
        int n=matrix[0].size();
        if(m==0 || n==0)return 0;
        vector<vector<int>>dp(m,vector<int>(n,0));
       
        for(int j=0;j<n;j++)
           if(matrix[0][j]==‘1‘)dp[0][j]=1;
        for(int j=0;j<n;j++)
        {
        for(int i=1;i<m;i++)
        {
            if(matrix[i][j]==‘1‘)dp[i][j]=dp[i-1][j]+1;
        }
        }
        int max_area=0;
        for(int i=0;i<m;i++)
            max_area=max(max_area,largestRectangleArea(dp[i]));
            
        return max_area;
    }