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Grokking the Coding Interview Patterns in Go

Solution: Number of Wonderful Substrings

Explore the method to count wonderful substrings where at most one letter appears an odd number of times. Learn to implement a hash map with bitmasking to efficiently track and count substring parities, optimizing for time and space complexity. This lesson helps develop skills for solving string and hashing problems 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: ...