CS210L-Project 3 Autocomplete Me Solved

The purpose of this assignment is to write a program to implement autocomplete for a given set of N strings and nonnegative weights. That is, given a prefix, find all strings in the set that start with the prefix, in descending order of weight.

Autocomplete is an important feature of many modern applications. As the user types, the program predicts the complete query (typically a word or phrase) that the user intends to type. Autocomplete is most effective when there are a limited number of likely queries. For example, the Internet Movie Database uses it to display the names of movies as the user types; search engines use it to display suggestions as the user enters web search queries; cell phones use it to speed up text input.

 

In these examples, the application predicts how likely it is that the user is typing each query and presents to the user a list of the top-matching queries, in descending order of weight. These weights are determined by historical data, such as box office revenue for movies, frequencies of search queries from other Google users, or the typing history of a cell phone user. For the purposes of this assignment, you will have access to a set of all possible queries and associated weights (and these queries and weights will not change).

The performance of autocomplete functionality is critical in many systems. For example, consider a search engine which runs an autocomplete application on a server farm. According to one study, the application has only about 50ms to return a list of suggestions for it to be useful to the user. Moreover, in principle, it must perform this computation for every keystroke typed into the search bar and for every user!

In this assignment, you will implement autocomplete by sorting the queries in lexicographic order; using binary search to find the set of queries that start with a given prefix; and sorting the matching queries in descending order by weight.

Problem 1. (Autocomplete Term) Implement an immutable comparable data type Term in Term.java that represents an autocomplete term: a string query and an associated real-valued weight. You must implement the following API, which supports comparing terms by three different orders: lexicographic order by query string (the natural order); in descending order by weight (an alternate order); and lexicographic order by query string but using only the first r characters (a family of alternate orderings). The last order may seem a bit odd, but you will use it in Problem 3 to find all terms that start with a given prefix (of length r).

method                                                                           description
Term(String query)
initialize a term with the given query string and zero weight
Term(String query, long weight)
initialize a term with the given query string and weight
int compareTo(Term that)
compare the terms in lexicographic order by query
static Comparator<Term> byReverseWeightOrder()
for comparing terms in descending order by weight
static Comparator<Term> byPrefixOrder(int r)
for comparing terms in lexicographic order but using only the first r characters of each query
String toString()
a string representation of the term
Corner cases. The constructor should throw a java.lang.NullPointerException if query is null and a java.lang.IllegalArgumentException if weight is negative. The byPrefixOrder() method should throw a java.lang.IllegalArgumentException if r is negative.

Performance requirements. The string comparison functions should take time proportional to the number of characters needed to resolve the comparison.

$ java Term data/cities.txt 5 Top 5 by lexicographic order:

2200                         ’s Gravenmoer, Netherlands

19190                       ’s-Gravenzande, Netherlands

134520 ’s-Hertogenbosch, Netherlands

3628                        ’t Hofke, Netherlands

246056 A Coru a , Spain

Top 5 by reverse-weight order:

14608512                                  Shanghai, China

13076300                                      Buenos Aires, Argentina

12691836                                Mumbai, India

12294193                                              Mexico City, Distrito Federal, Mexico

11624219                                    Karachi, Pakistan
Problem 2. (Binary Search Deluxe) When binary searching a sorted array that contains more than one key equal to the search key, the client may want to know the index of either the first or the last such key. Accordingly, implement a library of static methods BinarySearchDeluxe.java with the following API:

method                                                                                                   description
static int firstIndexOf(Key[] a, Key key, Comparator<Key> c)
the index of the first key in a[] that equals the search key, or -1 if no such key
static int lastIndexOf(Key[] a, Key key, Comparator<Key> c)
the index of the last key in a[] that equals the search key, or -1 if no such key
Corner cases. Each static method should throw a java.lang.NullPointerException if any of its arguments is null. You should assume that the argument array is in sorted order (with respect to the supplied comparator).

Performance requirements. The firstIndexOf() and lastIndexOf() methods should make at most 1 + dlogNe compares in the worst case, where N is the length of the array. In this context, a compare is one call to comparator.compare().

$ java BinarySearchDeluxe data/wiktionary.txt cook

3

Problem 3. (Autocomplete) In this part, you will implement a data type that provides autocomplete functionality for a given set of string and weights, using Term and BinarySearchDeluxe. To do so, sort the terms in lexicographic order; use binary search to find the set of terms that start with a given prefix; and sort the matching terms in descending order by weight. Organize your program by creating an immutable data type Autocomplete in Autocomplete.java with the following API:

method                                                     description
Autocomplete(Term[] terms)
initialize the data structure from the given array of terms
Term[] allMatches(String prefix)
all terms that start with the given prefix, in descending order of weight
int numberOfMatches(String prefix)
the number of terms that start with the given prefix
Corner cases. The constructor and each method should throw a java.lang.NullPointerException if its argument is null.

Performance requirements. The constructor should make proportional to N logN compares (or better) in the worst case, where N is the number of terms. The allMatches() method should make proportional to logN +M logM compares (or better) in the worst case, where M is the number of matching terms. The numberOfMatches() method should make proportional to logN compares (or better) in the worst case. In this context, a compare is one call to any of the compare() or compareTo() methods defined in Term.

$ java Autocomplete data/cities.txt 7

M

<enter>

12691836                                Mumbai, India

12294193                                                                Mexico City, Distrito Federal, Mexico

10444527                                     Manila, Philippines

10381222                                 Moscow, Russia

3730206 Melbourne, Victoria, Australia

3268513 Montr al , Quebec, Canada

3255944 Madrid, Spain

Al M

<enter>

431052 Al Ma allah al Kubr , Egypt

420195 Al Man rah , Egypt

290802 Al Mubarraz, Saudi Arabia

258132 Al Mukall , Yemen 227150 Al Miny , Egypt

128297 Al Man qil , Sudan

99357                       Al Ma ar yah , Egypt

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