# Isomorphic Words

### Class

public class IsomorphicWords { public int countPairs(String[] words) { // fill in code here } }

## Problem Statement

Two words are called isomorphic if the letters in one word can be remapped to get the second word. Remapping a letter means replacing all occurrences of it with another letter. The ordering of the letters remains unchanged. No two letters may map to the same letter, but a letter may map to itself.

For example, the words "abca" and "zbxz" are isomorphic because we can map 'a' to 'z', 'b' to 'b' and 'c' to 'x'.

Given a `String[] words`, return how many (unordered) pairs of words are isomorphic.

### Constraints

• `words` will contain between 2 and 50 elements, inclusive.

• Each element of `words` will contain between 1 and 50 lowercase letters ('a'-'z'), inclusive.

• All elements of `words` will have the same length.

• There will be no duplicates in `words`.

### Examples

1. ```
{"abca", "zbxz", "opqr"}

Returns: 1

```
"abca" and "zbxz" are isomorphic, but none of the two is isomorphic with "opqr".

2. ```
{"aa", "ab", "bb", "cc", "cd"}

Returns: 4

```
The four isomorphic pairs are {"aa", "bb"}, {"aa", "cc"}, {"bb", "cc"} and {"ab", "cd"}.

3. ```