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Grokking the Coding Interview Patterns in C#

Number of Wonderful Substrings

Understand how to identify and count wonderful substrings defined by character frequency conditions in a string. Explore using hash maps to efficiently track character occurrences and solve this substring counting challenge in C#.

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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 ...