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# 0205. Isomorphic Strings

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

## Description

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 * 104`
* `t.length == s.length`
* `s` and `t` consist of any valid ascii character.

## ac

```java
class Solution {
    public boolean isIsomorphic(String s, String t) {
        // edge cases
        if (s.length() != t.length()) return false;

        Map<Character, Character> map = new HashMap<>();
        Set<Character> set = new HashSet<>();
        for (int i = 0; i < s.length(); i++) {
            char cs = s.charAt(i);
            char ct = t.charAt(i);
            if (!map.containsKey(cs)) {
                if (set.contains(ct)) return false;
                map.put(cs, ct);
                set.add(ct);
            } else {
                if (map.get(cs) != ct) return false;
            }
        }

        return true;
    }
}
```