Leetcode 205: Isomorphic Strings

you have checked that for 1 string only, ie is s isomorphic to t or not? you need to check that also for t, ie is t isomorphic to s or not?

class Solution(object):
    def isIsomorphic(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        dict = {}
        dict2 = {}
        
        if len(s)==0 or len(t)==0:
            return False
        if len(s)!= len(t):
            return False
        for a,b in zip(s,t):
            if a not in dict:
                dict[a]=b
            else:
                if dict[a]!=b:
                    return False
            if b not in dict2:
                dict2[b] = a
            else:
                if dict2[b]!=a:
                    return False
        return True

As mentioned in the problem description:

No two characters may map to the same character

For input s = badc and t = baba, letter b and d in s both map to letter b in t, which violated the rule and should return false.

As mentioned by bui, we can add a condition in the else clause, to make sure values in the dict are unique:

class Solution(object):
    def isIsomorphic(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """
        dict = {}
        
        if len(s)==0 or len(t)==0:
            return False
        
        for i in range(len(s)):
            if s[i] in dict:
                if dict[s[i]] != t[i]:
                    return False
            else:
                if t[i] in dict.values():  
                    return False
                dict[s[i]] = t[i]
        return True