# LeetCode 205. Isomorphic Strings

## Description

https://leetcode.com/problems/isomorphic-strings/

Given two strings s and tdetermine if they are isomorphic.

Two strings s and t 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

Constraints:

• 1 <= s.length <= 5 * 104
• t.length == s.length
• s and t consist of any valid ascii character.

## Explanation

First, check if s and t have the same number of unique characters. Second, check if the orders of characters from two strings match. Third, check if each mapping character has the same number of occurrences.

## Python Solution

class Solution:
def isIsomorphic(self, s: str, t: str) -> bool:

counter1 = collections.Counter(s)
counter2 = collections.Counter(t)

if len(counter1) != len(counter2):
return False

mapping = {}

for c1, c2 in zip(s, t):
if c1 not in mapping:
mapping[c1] = c2
else:
if c2 != mapping[c1]:
return False

if counter1[c1] != counter2[c2]:
return False

return True

• Time Complexity: ~N
• Space Complexity: ~N