Maximal Rectangle in given matrix with 1,0(cpp, leetcode)

==============================================

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

Example:

Input:
[
  ["1","0","1","0","0"],
  ["1","0","1","1","1"],
  ["1","1","1","1","1"],
  ["1","0","0","1","0"]
]
Output: 6

========================================================================================

code ....

class Solution {
public:
    int largestRectangleArea(vector<int>& a)
    {
        if(a.size()==0)
            return 0;
       else if(a.size()==1)
           return a[0];
        
        stack <int>s;
        int i=0;
        int maxm=0;
         int area=0;
        
        while(i<a.size())
       {
           if(s.empty() || a[i]>=a[s.top()])
           {
               s.push(i);
               i++;
           } 
           else
           {
               int top=s.top();
               s.pop();
               
               if(s.empty())
               {
                   area=i*a[top];
               }
               else
               {
                   area=a[top]*(i-s.top()-1);
               }
               
               maxm=max(maxm,area);              
           }
       }
        while(!s.empty())
        {
           
             int top=s.top();
               s.pop();
               
               if(s.empty())
               {
                   area=i*a[top];
               }
               else
               {
                   area=a[top]*(i-s.top()-1);
               }
               
               maxm=max(maxm,area);
        }
        return maxm;      
    }
    
    int maximalRectangle(vector<vector<char>>& matrix)
    {
        if(matrix.size()==0)
            return 0;
        
    
        
        vector<int>t;
        t.resize(matrix[0].size(),0);
        
        // memset(t,0,sizeof(t));
        int maxm=0;
        
        for(int i=0;i<matrix.size();i++)
        {
            for(int j=0;j<matrix[0].size();j++)
            {
                if(matrix[i][j]=='0')
                    t[j]=0;
                else
                    t[j]++;
                    
            }
            
            int x=largestRectangleArea(t);
            maxm=max(maxm,x);     
            
        }              
        return maxm;
        
        
    }
};