Isomorphic String

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.

这里的对应关系说的是s[i]对应t[i]，而t[i]不一定需要对应s[i]但是这个对应关系必须是唯一不改变的，所以这里最简单清晰的逻辑就是先从s->t的关系利用哈希表扫描检查一遍，再用t->s的关系用另外一个哈希表扫描检查一遍，如果符合逻辑就输出True，当然这里也可以简化到一遍扫描，但是个人觉得逻辑不如两遍这么清晰直接，下面是代码

class Solution(object):
    def isIsomorphic(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        n = len(s)
        leftChecker = {}
        for i in xrange(n):
            if s[i] not in leftChecker:
                leftChecker[s[i]] = t[i]
            elif leftChecker[s[i]] != t[i]:
                return False

        rightChecker = {}
        for i in xrange(n):
            if t[i] not in rightChecker:
                rightChecker[t[i]] = s[i]
            elif rightChecker[t[i]] != s[i]:
                return False

        return True