"""File:     dfs.py
   Purpose:  Implement depth-first search of a digraph in Python

   Run:      python dfs.py

   Input:    Number of vertices in digraph
             Adjacency matrix of digraph

   Output:   Order in which DFS visits the vertices
"""
#----------------------------------------------------------------------
def get_matrix(n):
   """Read in and return a matrix of ints with n rows and n columns"""
   mat = []
   print "Enter the rows of the matrix, one row per line"
   for i in range(n):
      row_str = raw_input("")
      row_str_l = row_str.split()
      row = []
      for j in range(n):
         row.append(int(row_str_l[j]))
      mat.append(row)
   return mat

#----------------------------------------------------------------------
def print_matrix(mat, n):
   """Print a matrix with n rows and n columns"""
   for i in range(n):
      for j in range(n):
         print mat[i][j],
      print

#----------------------------------------------------------------------
def all_false(n):
   """Create a list, all of whose elements are False"""
   visited = []
   for i in range(n):
      visited.append(False)
   return visited

#----------------------------------------------------------------------
def print_list(l):
   """Print the contents of a list"""
   for i in l:
      print i,
   print

#----------------------------------------------------------------------
def depth_first_search(vert, mat, visited, n):
   """Visit the vertices in the digraph using depth-first search"""
   print "Visiting", vert
   visited[vert] = True
   for i in range(n):
      if mat[vert][i] == 1 and not visited[i]:
         depth_first_search(i, mat, visited, n)

#----------------------------------------------------------------------
n = int(raw_input("How many vertices\n   "))
mat = get_matrix(n)
print
print_matrix(mat, n)

visited = all_false(n)
#print
#print_list(visited)

print
depth_first_search(0, mat, visited, n)