## Description

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

Given two strings `s`

and `t`

, *determine 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 * 10`

^{4}`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