3581. Count Odd Letters from Number

You are given an integer n perform the following steps:

• Convert each digit of n into its lowercase English word (e.g., 4 → "four", 1 → "one").
• Concatenate those words in the original digit order to form a string s.

Return the number of distinct characters in s that appear an odd number of times.

Example 1:

Example 2:

Constraints:

• 1 <= n <= 109