Isomorphic Strings

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

## Blog link: https://code.dennyzhang.com/isomorphic-strings ## Basic Ideas: ## Build 2 dicts ## From s to t, and from t to s ## For any new item to compare, make sure it won't viloate any dict ## Complexity: Time O(n), Space O(1). (Keys of dictionary is quite limited) class Solution(object): def isIsomorphic(self, s, t): """ :type s: str :type t: str :rtype: bool """ m1, m2 = {}, {} for i in xrange(len(s)): ch1, ch2 = s[i], t[i] # mapping from s to t if m1.has_key(ch1): if m1[ch1] != ch2: return False else: m1[ch1] = ch2 # ab -> aa # mapping from t to s if m2.has_key(ch2): if m2[ch2] != ch1: return False else: m2[ch2] = ch1 return True

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