public int maximalRectangle(char[][] matrix) {

if (matrix==null || matrix.length==0 || matrix[0].length==0) return 0;

int m=matrix.length, n=matrix[0].length;

int[] h = new int[n];

int max = 0;

for (int i=0; i<m; i++){

for (int j=0; j<n; j++) h[j] = matrix[i][j]=='0' ? 0:h[j]+1;

max = Math.max(max, finder(h));

}

return max;

}

public int finder(int[] h){

Stack<Integer> left = new Stack<Integer>();

int r=0, max=0;

while (r<h.length){

if (left.isEmpty() || h[r]>=h[left.peek()]) left.push(r++);

else{

int height = h[left.pop()];

int len = left.isEmpty() ? r:r-left.peek()-1;

max = Math.max(max, height*len);

}

}

while (!left.isEmpty()){

int height = h[left.pop()];

int len = left.isEmpty() ? r:r-left.peek()-1;

max = Math.max(max, height*len);

}

return max;

}

}