isomorphism.py

#-------------------------------------------------------------------------------
# Name:        module1
# Purpose:
#
# Author:      Aravinthan
#
# Created:     11/02/2018
# Copyright:   (c) Aravinthan 2018
# Licence:     <your licence>
#-------------------------------------------------------------------------------

MAX_CHARS = 256

# This function returns true if str1 and str2 are isomorphic
def isomorphic(string1, string2):
	m = len(string1)
	n = len(string2)

	# Length of both strings must be same for one to one
	# corresponance
	if m != n:
		return "Not isomorphic."

	# To mark visited characters in str2
	marked = [False] * MAX_CHARS

	# To store mapping of every character from str1 to
	# that of str2. Initialize all entries of map as -1
	map = [-1] * MAX_CHARS

	# Process all characters one by one
	for i in xrange(n):

		# if current character of str1 is seen first
		# time in it.
		if map[ord(string1[i])] == -1:

			# if current character of st2 is already
			# seen, one to one mapping not possible
			if marked[ord(string2[i])] == True:
				return "Not isomorphic."

			# Mark current character of str2 as visited
			marked[ord(string2[i])] = True

			# Store mapping of current characters
			map[ord(string1[i])] = string2[i]

		# If this is not first appearance of current
		# character in str1, then check if previous
		# appearance mapped to same character of str2
		elif map[ord(string1[i])] != string2[i]:
			return "Not isomorphic."

	return True

# Driver program
print isomorphic("1232","2342")