A wonderful string is a string where at most one letter appears an odd number of times.

- For example, `"ccjjc"` and `"abab"` are wonderful, but `"ab"` is not.

Given a string `word` that consists of the first ten lowercase English letters (`'a'` through `'j'`), return the number of wonderful non-empty substrings in `word`. If the same substring appears multiple times in `word`, then count each occurrence separately.

A substring is a contiguous sequence of characters in a string.

Example 1:

    Input: word = "aba"

    Output: 4

    Explanation: The four wonderful substrings are underlined below:

    - "aba" -> "a"

    - "aba" -> "b"

    - "aba" -> "a"

    - "aba" -> "aba"

Example 2:

    Input: word = "aabb"

    Output: 9

    Explanation: The nine wonderful substrings are underlined below:

    - "aabb" -> "a"

    - "aabb" -> "aa"

    - "aabb" -> "aab"

    - "aabb" -> "aabb"

    - "aabb" -> "a"

    - "aabb" -> "abb"

    - "aabb" -> "b"

    - "aabb" -> "bb"

    - "aabb" -> "b"

Example 3:

    Input: word = "he"

    Output: 2

    Explanation: The two wonderful substrings are underlined below:

    - "he" -> "h"

    - "he" -> "e"

Constraints:

- `1 <= word.length <= 105`
- `word` consists of lowercase English letters from `'a'` to `'j'`.