Maximal Rectangle

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing all ones and return its area.

class Solution {    
public:
    int maximalRectangle(vector<vector<char> > &matrix) 
    {
        int m=matrix.size();
        if(m==0) return 0;
        
        int n=matrix[0].size();        
        int ** seq=new int*[m];
        for(int i=0;i<m;i++)
            seq[i]=new int[n];
        for(int i=0;i<m;i++)
        {
            int index=0;
            for(int j=0;j<n;j++)
            {
                seq[i][j]=matrix[i][j]-'0';
                if(j>0 && matrix[i][j]=='1' && matrix[i][j-1]=='1')
                    seq[i][j]=seq[i][j-1]+1;
            }
        }
        int max=0;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                int min=seq[j][i];
                for(int k=j;k<m;k++)
                {
                    if(min>seq[k][i]) min=seq[k][i];
                    if(min*(k-j+1)>max) max=min*(k-j+1);                    
                }
            }
        }
        return max;
    }
};