Project 3 (Autocomplete Me)

CS210 Project 3 (Autocomplete Me)
This document only contains the description of the project and the project problems. For the programming exercises on
concepts needed for the project, please refer to the project checklist .
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
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
int compareTo(Term that) compare the terms in lexicographic order by query
String toString() a string representation of the term
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CS210 Project 3 (Autocomplete Me) Swami Iyer
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 C o r u 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 + dlog Ne 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
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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 log N compares (or better) in the worst case,
where N is the number of terms. The allMatches() method should make proportional to log N +M log M compares (or better)
in the worst case, where M is the number of matching terms. The numberOfMatches() method should make proportional to
log N 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.
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CS210 Project 3 (Autocomplete Me) Swami Iyer
$ 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 M o n t r a l , Quebec , Canada
3255944 Madrid , Spain
Al M
< enter
431052 Al M a a l l a h al K u b r , Egypt
420195 Al M a n r a h , Egypt
290802 Al Mubarraz , Saudi Arabia
258132 Al M u k a l l , Yemen
227150 Al M i n y , Egypt
128297 Al M a n q i l , Sudan
99357 Al M a a r y a h , Egypt
<ctrl -d
Acknowledgements This project is an adaptation of the Autocomplete Me assignment developed at Princeton University
by Matthew Drabick and Kevin Wayne.
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