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Find the Longest Even-Length Word

Walmart LabsSoftware Engineer · Technical Screen
EasySoftware EngineerTechnical ScreenCoding & Algorithms

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Tests string tokenization, linear scanning, tie-breaking logic, and handling of edge cases such as absent matches or irregular whitespace.

Problem Statement

You are given a string sentence containing words separated by spaces. Your task is to find the longest word in the sentence that has an even number of characters.

  • If there are multiple even-length words with the same maximum length, return the word that appears first in the sentence.
  • If no even-length word exists in the sentence, return "00".

A word is defined as a maximal sequence of non-space characters.

Function Signature

def longest_even_word(sentence: str) -> str:
    pass

Input & Output

  • Input: sentence (a string of length n containing English letters, digits, and spaces).
  • Output: A string representing the longest even-length word found, or "00" if none exist.

Constraints

  • 1 <= len(sentence) <= 10^5
  • sentence may contain leading, trailing, or consecutive spaces.
  • Words consist of alphanumeric characters.

Examples

Example 1

Input: sentence = "Time to write great code"
Output: "Time"
Explanation:
- "Time": length 4 (even)
- "to": length 2 (even)
- "write": length 5 (odd)
- "great": length 5 (odd)
- "code": length 4 (even)

Both "Time" and "code" have the maximum even length of 4. We return "Time" because it appears first.

Example 2

Input: sentence = "It is a pleasant day today"
Output: "pleasant"
Explanation:
- "It": length 2 (even)
- "is": length 2 (even)
- "a": length 1 (odd)
- "pleasant": length 8 (even)
- "day": length 3 (odd)
- "today": length 5 (odd)

The longest even-length word is "pleasant" with length 8.

Example 3

Input: sentence = "You can do it"
Output: "do"
Explanation:
"do" (length 2) and "it" (length 2) are even. "do" appears first.

Example 4

Input: sentence = "The red fox jumps"
Output: "00"
Explanation:
Lengths are 3, 3, 3, 5. None are even, so return "00".

Edge Cases to Consider

  • Sentences with multiple spaces between words or leading/trailing whitespace.
  • Sentences where every word has an odd length.
  • Sentences consisting only of whitespace characters.
  • Sentences with only a single word.

Hints

Hint 1

Tokenize the sentence by splitting on whitespace to handle irregular spacing cleanly.

Hint 2

Track both the longest even word found so far and its length; update them only when you encounter a word with an even length strictly greater than the current maximum.

Hint 3

Initialize the result to "00" so you can return it directly if no even-length word is found.

Follow-up questions

  • How would you optimize this to run in O(1) auxiliary space without creating an intermediate list of words?
  • How should your function handle attached punctuation marks (such as commas or periods) without counting them toward word length?
  • If the input were a stream of characters too large to fit in memory, how would you adapt your parsing logic?