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. Example 1: Input: s  egg, t  add Output: true Example 2: Input: s  foo, t  bar Output: false Example 3: Input: s  paper, t  title Output: true Reference: https:leetcode.comproblemsisomorphicstringsdescription :type s: str :type t: str :rtype: bool
def is_isomorphic(s, t):
    """
    :type s: str
    :type t: str
    :rtype: bool
    """
    if len(s) != len(t):
        return False
    dict = {}
    set_value = set()
    for i in range(len(s)):
        if s[i] not in dict:
            if t[i] in set_value:
                return False
            dict[s[i]] = t[i]
            set_value.add(t[i])
        else:
            if dict[s[i]] != t[i]:
                return False
    return True
