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Leetcode Problem 1189: Maximum Number of Balloons

Given a string text, you want to use the characters of text to form as many instances of the word “balloon” as possible. Each character in the string text can only be used once. Return the maximum number of instances that can be formed.

Clarifying Questions

  1. Input: What is the range of the length of the input string?
    • Generally, problems of this nature will have strings of length up to 10^4 or similar, but it’s good to confirm.
  2. Case Sensitivity: Should the word “balloon” be case-sensitive?
    • Assuming if “balloon” must be exactly in lower-case.
  3. Character Set: Are the characters in text guaranteed to be alphabetic or could there be other types of characters?
    • Assuming the input will only contain alphabetic characters.

Code

def maxNumberOfBalloons(text: str) -> int:
    from collections import Counter
    
    # Count all characters in the input text
    count = Counter(text)
    
    # The word we need to form is "balloon"
    balloon_count = Counter("balloon")
    
    # Find the minimum number of times we can form "balloon"
    return min(count[char] // balloon_count[char] for char in balloon_count)

# Example usage
print(maxNumberOfBalloons("nlaebolko"))  # Output should be 1
print(maxNumberOfBalloons("loonbalxballpoon"))  # Output should be 2
print(maxNumberOfBalloons("leetcode"))  # Output should be 0

Strategy

  1. Counting Characters: Use Python’s collections.Counter to count the frequency of each character in the input string text.
  2. Character Requirements: Similarly, count the frequency of each character in the word “balloon”.

  3. Compute Instances: For each character in the word “balloon”, determine how many times it can be used (i.e., text_count[char] // balloon_count[char]).

  4. Minimum Constraint: The maximum number of “balloon”s that can be formed is limited by the least available required character based on its required frequency.

Time Complexity

This solution should be efficient even for the upper limits of typical input sizes in interview scenarios.

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