implement sorting algorithms for the autocomplete application.
java代写/算法代写/algorithm代写: 这是一个通过java实现类似google搜索引擎的搜索自动填充功能，该项目对自动补充算法要求有一定的理解，对算法基础和java基础要求较高
1. Purpose
The purpose of this assignment is to implement sorting algorithms for the autocomplete
application.
2. Description
Write a program to implement autocomplete for a given set of N terms, where a term
is a query string and an associated nonnegative weight. That is, given a prefix, find all
queries that start with the given prefix, in descending order of weight.
Autocomplete is pervasive in 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
2
2
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 terms by query
string (with running time O(N log N) in sorting, or even better, where N is the of
terms); binary searching to find all query strings that start with a given prefix (with
running time O(log N)); and sorting the matching terms by weight (with running time
O(M log M) in sorting, where M is the number of matching terms). Finally display
results for the user. The following shows the top seven queries (city names) that start
with AI M with weights equal to their populations.
2.1. Part 1: autocomplete term (60 pts)
Write an immutable data type Term.java that represents an autocomplete term: a query
string and an associated integer 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 Part
3 to find all query strings that start with a given prefix (of length r).
public class Term implements Comparable
/* Initializes a term with the given query string and weight. */
public Term(String query, long weight)
/* Compares the two terms in descending order by weight. */
public static Comparator
/* Compares the two terms in lexicographic order but using only the first
r characters of each query. */
public static Comparator
/* Compares the two terms in lexicographic order by query. */
public int compareTo(Term that)
3
3
// Returns a string representation of this term in the following format:
// weight (i.e., ??.toString()), followed by a tab, followed by query.
public String toString()
}
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.
2.2. Part 2: binary search (30 pts)
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 the following API:
public class BinarySearchDeluxe {
/* Returns the index of the first key in a[] that equals the search key,
or -1 if no such key. */
public static
comparator)
/* Returns the index of the last key in a[] that equals the search key,
or -1 if no such key. */
public static
comparator)
}
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 + ⌈log2 N⌉ compares in the worst case, where N is the length of the
array. In this context, a compare is one call to comparator.compare().
2.3. Part 3: autocomplete (70 pts)
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 all query strings
4
4
that start with a given prefix; and sort the matching terms in descending order by
weight. Organize your program by creating an data type Autocomplete with the
following API:
public class Autocomplete { // implement sorting algorithm in this class
/* Initializes the data structure from the given array of terms. */
public Autocomplete(Term[] terms)
/* Returns all terms that start with the given prefix, in descending
order of weight. */
public Term[] allMatches(String prefix)
}
Corner cases. The constructor should throw a java.lang.NullPointerException if its
argument is null or if any of the entries in its argument array are null. 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. In this context,
a compare is one call to any of the compare()or compareTo() methods defined in Term.
2.4. Input format for testing (30 pts)
We provide a number of sample input files for testing. Each file consists of an
integer N followed by N pairs of query strings and nonnegative weights. There is one
pair per line, with the weight and string separated by a tab. A weight can be any
integer between 0 and 2^63 − 1. A query string can be an arbitrary sequence of
Unicode characters, including spaces (but not newlines).
• The file wiktionary.txt contains the 10,000 most common words in Project
Gutenberg, with weights proportional to their frequencies.
• The file cities.txt contains over 90,000 cities, with weights equal to their
populations.
% more wiktionary.txt
10000
5627187200 the
3395006400 of
2994418400 and
2595609600 to
1742063600 in
1176479700 i
1107331800 that
1007824500 was
% more cities.txt
93827
14608512 Shanghai, China
13076300 Buenos Aires, Argentina
12691836 Mumbai, India
12294193 Mexico City, Distrito Federal, Mexico
11624219 Karachi, Pakistan
11174257 İstanbul, Turkey
10927986 Delhi, India
10444527 Manila, Philippines
5
5
879975500 his
…
392323 calves
10381222 Moscow, Russia
…
2 Al Khāniq, Yemen
Below is a sample client that takes the name of an input file and an integer k as
command-line arguments. It reads the data from the file; then it repeatedly reads
autocomplete queries from standard input, and prints out the top k matching terms in
descending order of weight.
public static void main(String[] args) {
// always print messages on screen when debugging
// System.out.println(…);
// read in the terms from a file
String filename = args[0]; // first argument from command line
In in = new In(filename);
int N = in.readInt();
Term[] terms = new Term[N];
for (int i = 0; i < N; i++) {
long weight = in.readLong(); // read the next weight
in.readChar(); // scan past the tab
String query = in.readLine(); // read the next query
terms[i] = new Term(query, weight); // construct the term
}
// read in queries from standard input and print the top k matching terms
int k = Integer.parseInt(args[1]); // 2nd argument from command line
Autocomplete autocomplete = new Autocomplete(terms);
while (StdIn.hasNextLine()) {
String prefix = StdIn.readLine();
Term[] results = autocomplete.allMatches(prefix);
for (int i = 0; i < Math.min(k, results.length); i++)
System.out.println(results[i]);
}
}
Here are a few sample executions:
% java Autocomplete wiktionary.txt 5
auto
619695 automobile
424997 automatic
comp
13315900 company
7803980 complete
6038490 companion
5205030 completely
4481770 comply
the
5627187200 the
334039800 they
282026500 their
250991700 them
196120000 there
% java Autocomplete cities.txt 7
M
12691836 Mumbai, India
12294193 Mexico City, Distrito
Federal, Mexico
10444527 Manila, Philippines
10381222 Moscow, Russia
3730206 Melbourne, Victoria,
Australia
3268513 Montréal, Quebec, Canada
3255944 Madrid, Spain
Al M
431052 Al Maḩallah al Kubrá, Egypt
420195 Al Manşūrah, Egypt
290802 Al Mubarraz, Saudi Arabia
258132 Al Mukallā, Yemen
227150 Al Minyā, Egypt
first argument
2nd argument
defined in In.java, to read data
from files and URLs
defined in StdIn.java, to
read data from keyboard
6
6
128297 Al Manāqil, Sudan
99357 Al Maţarīyah, Egypt
Interactive GUI (optional, but fun and no extra work):
Compile AutocompleteGUI.java. The program takes the name of a file and an
integer k as command-line arguments and provides a GUI for the user to enter queries.
It presents the top k matching terms in real time. When the user selects a term, the
GUI opens up the results from a Google search for that term in a browser.
% java AutocompleteGUI cities.txt 7
3.
If your program does not compile, you receive zero points for that program. Additional
deductions:
1. (5 points) Your code does not follow the style guide discussed in class/textbook.
2. (30 points) Your code does not have author name, date, purpose of this program,
comments on the variables and methods, etc.
4.
One submission for a team. Zip/submit your entire project,
including Autocomplete.java, BinarySearchDeluxe.java, and Term.java. You may
NOT call any library functions other than those in java.lang and java.util. Finally,
submit a report file (10 points) and answer the following questions:
a) Known bugs limitations of this assignment.
b) Describe any serious problems you encountered.
c) List any other comments here. Feel free to provide any feedback on how much you
learned from doing the assignment, and whether you enjoyed doing it.