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Grokking the Coding Interview Patterns

Solution: Number of Wonderful Substrings

Explore how to count wonderful substrings in a string using a hash map combined with bitmasking techniques. This lesson helps you understand the approach to track character parity, update frequency counts, and calculate substring counts under the constraint that at most one character is allowed an odd count. By mastering this solution, you'll enhance problem-solving skills for complex substring and bit manipulation challenges commonly faced in coding interviews.

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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: ...