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Grokking the Coding Interview Patterns in JavaScript

Solution: Number of Wonderful Substrings

Explore how to find and count wonderful substrings in a string by using hash maps and bitmask techniques. Understand the logic of toggling bits to track character parity and efficiently determine substrings with limited odd occurrences. This lesson helps you apply these concepts to solve coding problems with constraints on character sets.

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Statement

A wonderful string is defined as a string in which at most one letter occurs an odd number of times.

For example:

  • The string “aabbc” is wonderful because only the letter 'c' appears an odd number of times.

  • The string “pqpq” is wonderful because all letters appear an even number of times.

  • The string “mn” is not wonderful because both 'm' and 'n' appear an odd number of times.

You are given a string word that consists of lowercase English letters from 'a' to 'j'. Your task is to return the total number of wonderful non-empty substringsA substring is any contiguous sequence of characters within the string. in word.

Note: If a substring appears multiple times, each occurrence should be counted separately.

Constraints: ...