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Grokking the Coding Interview Patterns

Solution: Bulls and Cows

Explore the Bulls and Cows problem and understand how to solve it using a single-pass hash map approach. This lesson guides you through counting bulls and cows by tracking unmatched digits, optimizing your algorithm design and application of hash maps for common coding interview challenges.

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Statement

You are playing a number guessing game called “Bulls and Cows” with a friend.

You write down a secret number, and your friend tries to guess it. After each guess, you provide a hint based on the following:

  • Bulls: The number of digits that are in the correct position in the guess.

  • Cows: The number of digits that are in both the secret and the guess but in different positions. (These are non-bull digits that could become bulls if rearranged.)

Your task is to return a hint for the guess, formatted as “xAyB”, where:

  • x is the number of bulls.

  • y is the number of cows.

Note: Both the secret number and the guess may contain duplicate digits.

Constraints:

  • 1<=1 <= secret.length, guess.length ...