Problem Statement  
Given a directed graph on n vertices, your task is to label its vertices as follows:
 
Definition  
 
Notes  
  int[] a comes before int[] b lexicographically if a[i] < b[i] , where i is the first position in which a and b differ.  
Constraints  
  m will contain between 1 and 50 elements, inclusive.  
  Each element of m will contain exactly n characters, where n is the number of elements in m.  
  Each character in each element of m will be '1' (one) or '0' (zero).  
  The ith character of the ith element of m will be '0'.  
Examples  
0)  
 
1)  
 
2)  
 
3)  
