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isomorphic-strings.py
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isomorphic-strings.py
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# Time: O(n)
# Space: O(1)
# Given two strings s and t, determine if they are isomorphic.
#
# Two strings are isomorphic if the characters in s can be replaced to get t.
#
# All occurrences of a character must be replaced with another character
# while preserving the order of characters. No two characters may map to
# the same character but a character may map to itself.
#
# For example,
# Given "egg", "add", return true.
#
# Given "foo", "bar", return false.
#
# Given "paper", "title", return true.
#
# Note:
# You may assume both s and t have the same length.
from itertools import izip # Generator version of zip.
class Solution(object):
def isIsomorphic(self, s, t):
"""
:type s: str
:type t: str
:rtype: bool
"""
if len(s) != len(t):
return False
s2t, t2s = {}, {}
for p, w in izip(s, t):
if w not in s2t and p not in t2s:
s2t[w] = p
t2s[p] = w
elif w not in s2t or s2t[w] != p:
# Contradict mapping.
return False
return True
# Time: O(n)
# Space: O(1)
class Solution2(object):
def isIsomorphic(self, s, t):
if len(s) != len(t):
return False
return self.halfIsom(s, t) and self.halfIsom(t, s)
def halfIsom(self, s, t):
lookup = {}
for i in xrange(len(s)):
if s[i] not in lookup:
lookup[s[i]] = t[i]
elif lookup[s[i]] != t[i]:
return False
return True