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'.