LeetCode642DesignSearchAutoCompleteSystem -Solution to LeetCode642 Design Search AutoComplete System

Summary

This video tutorial explains how to design a search autocomplete system similar to Google's. It covers the rules for returning the top three historically popular sentences based on frequency and ASCII values, and provides a step-by-step guide on implementing the system using an array of hashmaps to store and retrieve sentences and their frequencies.

Takeaways

• 😀 The video discusses designing a search autocomplete system similar to Google's.
• 🔍 Users input sentences ending with a hash (#), and the system returns the top three historically popular sentences that match the prefix.
• 🔢 The popularity or 'hot degree' of a sentence is determined by how many times it has been typed by users.
• 📈 If multiple sentences have the same hot degree, they are sorted lexicographically, with the smaller ASCII code coming first.
• 📚 The system requires a constructor function that initializes with an array of sentences and their corresponding frequencies.
• 📝 The system also includes a method to handle user input, recording the current sentence and updating the frequency of sentences in the database.
• 🔤 The input can include lowercase letters, spaces, or a hash, and the system must handle these inputs appropriately.
• 📌 The system uses an array of hashmaps, indexed by the first character of each sentence, to store and retrieve sentences and their frequencies.
• 🔎 When a user types a character, the system checks the corresponding hashmap for sentences that start with the current input string.
• 📊 The system sorts the matching sentences by frequency and lexicographical order, then returns the top three or as many as available.
• 🏁 When a user inputs a hash, the system ends the current search, updates the frequency of the current sentence, and returns an empty list.

Q & A

What is the main purpose of the system described in the script?

The main purpose of the system is to design a search autocomplete functionality for a search engine, similar to Google's auto search, where users can input a sentence and the system will suggest the top three historical hot sentences that are prefixes of the input.

What is a special character hash used for in this context?

In this context, the special character hash is used to signify the end of a user's input sentence, triggering the system to return the top three hot sentences based on the input.

How are the suggested sentences ranked in the system?

The suggested sentences are ranked based on their 'hot degree,' which is the number of times the user has typed the exact same sentence before. If multiple sentences have the same hot degree, they are sorted lexicographically based on their ASCII values.

What happens when the user types a special character hash?

When the user types a special character hash, it indicates the end of the search. In this case, the system needs to return an empty list because it signifies the end of the input sentence.

How does the system handle less than three historical hot sentences?

If there are less than three historical hot sentences, the system will return as many as it can, based on the input prefix and the hot degree of those sentences.

What is the role of the constructor function in the system?

The constructor function initializes the system by taking in an array of strings (sentences) and an array of integers (frequencies), setting up the data structure for tracking the frequency of each sentence.

What is the significance of the second method 'list of string input' in the system?

The second method 'list of string input' is crucial for processing the user's input in real-time. It records the current string and updates the system's historical data, returning the top three hot sentences based on the current input.

How does the system ensure that the top three hot sentences are updated in real-time?

The system updates the top three hot sentences in real-time by recording the current string as the user types and checking against the historical data. It then sorts and returns the top three sentences based on their hot degree and lexicographical order if necessary.

What is the data structure used to store the sentences and their frequencies?

The data structure used is an array of hash maps, where each index in the array corresponds to a starting character of a sentence, and the hash map stores the sentences and their frequencies.

How does the system handle the input of lowercase letters, spaces, or special characters?

The system handles the input by adding the characters to the current string and checking the historical data for sentences that start with the current string. It then updates the frequencies and returns the top three hot sentences accordingly.