What is the optimal time complexity of solving Phone Directory?

The optimized solution achieves a time complexity of O(n) by using sorting, mathematical shortcuts, or hash table lookups.

What is the auxiliary space complexity for Phone Directory?

The space complexity is O(1) since we only use a minimal/constant amount of extra memory for tracking variables (or auxiliary space if dynamic structures are allocated).

What are the typical edge cases we must handle in Phone Directory?

Key edge cases include empty collections, negative or large bounds causing integer overflow, arrays with only one element, or inputs where target criteria are not met.

How can we optimize the brute force approach for Phone Directory?

Brute force methods often inspect all possible combinations. We optimize this by sorting the input list to enable binary search, or tracking processed items in a set to avoid redundant nested loop lookups.

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Competitive ProgrammingEasy

Phone Directory

Learn how to solve the 'Phone Directory' problem. This detailed resource details brute force and optimized approaches.

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Problem Statement

Easy

Write a function phone_directory(contacts, query) that takes a list of unique strings contacts and a query string query. It should return a list of lists of strings, where the ith list contains the sorted contacts that match the prefix of query up to length i+1 (1-indexed). If no contact matches, return an empty list for that prefix.

Constraints

•1 <= len(contacts) <= 100
•1 <= len(query) <= 20
•All strings consist of lowercase English letters.

Examples

Example 1

Input

phone_directory(['geeikist', 'geeksforgeeks', 'geeksfortest', 'geeky'], 'gee')

Output

[['geeikist', 'geeksforgeeks', 'geeksfortest', 'geeky'], ['geeikist', 'geeksforgeeks', 'geeksfortest', 'geeky'], ['geeikist', 'geeksforgeeks', 'geeksfortest', 'geeky']]

Explanation

For 'g', 'ge', and 'gee', all 4 contacts match prefix and are returned in sorted order.

Example 2

Input

phone_directory(['mobile', 'mouse', 'moneypot', 'monitor', 'mousepad'], 'mouse')

Output

[['mobile', 'monitor', 'moneypot', 'mouse', 'mousepad'], ['mobile', 'monitor', 'moneypot', 'mouse', 'mousepad'], ['mouse', 'mousepad'], ['mouse', 'mousepad'], ['mouse', 'mousepad']]

Explanation

For prefix 'm' and 'mo', all contacts match. For 'mou', 'mous', and 'mouse', only 'mouse' and 'mousepad' match.

Need a Hint?

Analyze the input constraints. Try sorting first (O(n log n)) or using a hash map/set to track seen elements in O(n) time.

Edge Cases to Watch

Empty list or null input variables
Single item lists/arrays
Extremely large input bounds causing integer or stack overflow

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