README.md

205. 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.

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

Note:

You may assume both s and t have the same length.

Solutions (Python)

1. Brute Force

class Solution:
    def isIsomorphic(self, s: str, t: str) -> bool:
        checked = set()
        for i in range(len(s)):
            if s[i] not in checked:
                for j in range(i + 1, len(s)):
                    if s[j] == s[i] and t[j] != t[i] or s[j] != s[i] and t[j] == t[i]:
                        return False
                checked.add(s[i])
        return True

2. HashMap

class Solution:
    def isIsomorphic(self, s: str, t: str) -> bool:
        smap = {}
        tset = set()

        for cs, ct in zip(s, t):
            if (cs in smap) != (ct in tset):
                return False
            elif cs not in smap:
                smap[cs] = ct
                tset.add(ct)
            elif smap[cs] != ct:
                return False

        return True