Leetcode: Isomorphic Strings II

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.

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
                m1[ch1] = ch2

            # ab -> aa
            # mapping from t to s
            if m2.has_key(ch2):
                if m2[ch2] != ch1:
                    return False
                m2[ch2] = ch1
        return True

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