What is the method to find the largest word in a dictionary by deletion?
The task is to determine the longest word in a dictionary that can be formed by deleting characters from a source string. It tests string processing logic.
Why Interviewers Ask This
This question evaluates a candidate's ability to process sequences and implement greedy algorithms. Interviewers want to see if you can efficiently compare a target string against a list of candidates without resorting to expensive operations. It also tests attention to detail regarding lexicographical ordering when multiple words have the same maximum length.
How to Answer This Question
Propose a solution that iterates through each word in the dictionary. For each word, check if it is a subsequence of the source string using a two-pointer approach. Keep track of the best word found so far based on length, and break ties using lexicographical order. Explain why this linear scan is optimal. Discuss the time complexity relative to the total number of characters in the dictionary.
Key Points to Cover
- Using the two-pointer technique for subsequence checking
- Comparing words based on length and lexicographical order
- Ensuring linear time complexity per dictionary word
- Handling edge cases like empty dictionaries
Sample Answer
I would iterate through every word in the given dictionary. For each word, I'll use a two-pointer technique to verify if it is a subsequence of the source string. One pointer tracks the source string, and the other tracks the current dictionary word. If characters match, I advance both pointers; otherwise, I only advance the source pointer. If I successfully traverse the entire dictionary word, it is a valid candidate. I maintain a variable for the 'best' word, updating it if the current word is longer or if it is of equal length but lexicographically smaller. This approach ensures an efficient O(N*M) solution where N is the source length and M is the total characters in the dictionary.
Common Mistakes to Avoid
- Using substring checks instead of subsequence logic
- Ignoring the tie-breaking rule for lexicographical order
- Failing to handle empty input strings correctly
- Inefficiently comparing characters inside nested loops
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