> For the complete documentation index, see [llms.txt](https://mayanktyagi3111.gitbook.io/interview-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mayanktyagi3111.gitbook.io/interview-prep/hashmap-and-hashset-and-sliding-window/isomorphic-strings.md).

# 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.

```java
public class Solution {
    // You may assume both s and t have the same length.
    public boolean isIsomorphic(String s, String t) {
        Map<Character, Integer> mapS = new HashMap<Character, Integer>();
        Map<Character, Integer> mapT = new HashMap<Character, Integer>();

        for (int i = 0; i < s.length(); i++) {
            int indexS = mapS.getOrDefault(s.charAt(i), -1);
            int indexT = mapT.getOrDefault(t.charAt(i), -1);

            if (indexS != indexT)
                return false;

            mapS.put(s.charAt(i), i);
            mapT.put(t.charAt(i), i);
        }

        return true;
    }
}
```