README.md

1915. Number of Wonderful Substrings

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'.

Solutions (Rust)

1. Solution

impl Solution {
    pub fn wonderful_substrings(word: String) -> i64 {
        let word = word.as_bytes();
        let mut count = [0; 1024];
        let mut mask = 0;
        let mut ret = 0;
        count[0] = 1;

        for i in 0..word.len() {
            mask ^= 1 << (word[i] - b'a');
            for j in 0..10 {
                ret += count[mask ^ (1 << j)];
            }
            ret += count[mask];
            count[mask] += 1;
        }

        ret
    }
}