public class Solution
extends Object
1915 - Number of Wonderful Substrings\.
Medium
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:
- "**a**ba" -> "a"
- "a**b**a" -> "b"
- "ab**a**" -> "a"
- "**aba**" -> "aba"
**Example 2:**
**Input:** word = "aabb"
**Output:** 9
**Explanation:** The nine wonderful substrings are underlined below:
- "**a**abb" -> "a"
- "**aa**bb" -> "aa"
- "**aab**b" -> "aab"
- "**aabb**" -> "aabb"
- "a**a**bb" -> "a"
- "a**abb**" -> "abb"
- "aa**b**b" -> "b"
- "aa**bb**" -> "bb"
- "aab**b**" -> "b"
**Example 3:**
**Input:** word = "he"
**Output:** 2
**Explanation:** The two wonderful substrings are underlined below:
- "**h**e" -> "h"
- "h**e**" -> "e"
**Constraints:**
* 1 <= word.length <= 105
* `word` consists of lowercase English letters from `'a'` to `'j'`.