README_EN.md

1915. Number of Wonderful Substrings

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Description

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

Python3

Java

JavaScript

/**
 * @param {string} word
 * @return {number}
 */
var wonderfulSubstrings = function(word) {
    let n = 1 << 10;
    let counts = new Array(n).fill(0);
    counts[0] = 1;
    let pre = 0;
    let ans = 0;
    for (let c of word) {
        let cur = c.charCodeAt(0) - 'a'.charCodeAt(0);
        pre ^= (1 << cur);
        ans += counts[pre];
        for (let i = 1; i < n; i <<= 1) {
            ans += counts[pre ^ i];
        }
        ++counts[pre];
    }
    return ans;
};

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