#!/usr/bin/env python
# encoding: utf-8

"""
undirect.py

Created by Michele Catasta on 2007-06-23.

Checks if a graph contained in a DIMACS .gr file is undirect.
Silent output if positive.

Usage: python undirect.py FILE_NAME.gr
"""

import sys
import os


def main():
	
	f = open(sys.argv[1],"r")
	
	# skips comments and additional infos
	while 1:
		start = f.tell()
		header = f.readline()[0:1]
		
		if header != 'a':
			pass
		else:
			f.seek(start)
			break
	
	i = iter(f)
	
	# undirectness check
	try:
		while True:
			oddline = i.next()
			evenline = i.next()
			
			a1, b1, w1 = oddline.split(" ")[1:4]
			b2, a2, w2 = evenline.split(" ")[1:4]
			
			if(a1 != a2 or b1 != b2 or w1 != w2):
				print "Given graph IS direct."
				break

	except StopIteration:
		pass

if __name__ == '__main__':
    main()