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Grokking the Coding Interview Patterns in C++

Solution: Number of Wonderful Substrings

Explore how to efficiently count wonderful substrings in a string where at most one character occurs an odd number of times. Learn to use hash maps and bitmask operations to track character frequencies and solve substring problems with optimized time and space complexity.

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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:

  • 1<=1 <= word.length <=103<= 10^3 ...