leetcode[85]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 largestRectangleArea(vector<int> &height) 
{
    if(height.empty())return 0;
    height.push_back(0);
    int maxRes=0;
    stack<int> sta;
    for (int i=0;i<height.size();i++)
    {
        int top;
        int newRes;
        while(!sta.empty()&&height[i]<height[sta.top()])
        {
            top=sta.top();
            sta.pop();
            newRes=(sta.empty()?i:(i-sta.top()-1))*height[top];
            maxRes=maxRes>newRes?maxRes:newRes;                
        }
        sta.push(i);
    }
    return maxRes;
}
int maximalRectangle(vector<vector<char> > &matrix) 
{
    if(matrix.empty())return 0;
    int m=matrix.size();
    if(matrix[0].empty())return 0;
    int n=matrix[0].size();
    int maximal=0;
    vector<vector<int>> d(m,vector<int> (n));
    for(int i=0;i<m;i++)
    {
        for(int j=0;j<n;j++)
        {
            if(i==0)d[i][j]=matrix[i][j]-'0';
            else 
            {
                if(matrix[i][j]=='1')
                {
                    d[i][j]=d[i-1][j]+matrix[i][j]-'0';
                }
                else
                {
                    d[i][j]=matrix[i][j]-'0';
                }
            }
        }
        int tmp=largestRectangleArea(d[i]);
        maximal=maximal>tmp?maximal:tmp;
    }
    return maximal;
}
};