Question

For Autocomplete.java, I am trying to implement a data type that provides autocomplete functionality for a given set of string and weights, using Term and BinarySearchDeluxe.. Should sort the terms in lexicographic order, use binary search to find the set of terms that start with given prefix, and sort matching terms in descending order by weight. Corner cases: Constructor and each method throws a java.lang.NullPointerException if argument is null. Constructor should make proportional N log N compares worst case scenario, N is number of terms. allMatches() should make proportional to logN + MlogM compares worst case scenario, M is # of matching terms. numberOfMatches() should be proportional to log N compares worst case. Comments are given above methods that need more work, look for "//?" which denotes areas that need to be filled.

Additional comments regarding methods that need work:

Method: Autocomplete(Term[] terms) … Description: Initialize data structure from given array of terms

Method: Term[] allMatches(String prefix) … Description: All terms that start with given prefix, by descending order of weight

Method: int numberOfMatches(String prefix) … Description: number of terms that start with given prefix

Below is what I have so far for Autocomplete.java:

import java.util.Arrays;
import java.util.Comparator;

public class Autocomplete {
private Term[] terms;

//data structure from given array of terms.
public Autocomplete(Term[] terms) {
//?
}

//terms start with given prefix, descending weight
public Term[] allMatches(String prefix) {
   //?
}

//Total number of terms with given prefix
public int numberOfMatches(String prefix) {
   //?
}

public static void main(String[] args) throws IOException{
String fname = args[0];
In in = new In(fname);
int N = in.readInt();
Term[] terms = new Term[N];
for (int i = 0; i < N; i++) {
long weight = in.readLong();
in.readChar();
String query = in.readLine();
terms[i] = new Term(query.trim(), weight);
}
int c = Integer.parseInt(args[1]);
Autocomplete autocomplete = new Autocomplete(terms);
while (StdIn.hasNextLine()) {
String prefix = StdIn.readLine();
Term[] results = autocomplete.allMatches(prefix);
for (int i = 0; i < Math.min(c, results.length); i++) {
System.out.println(results[i]);
}
}
}
}

Answer 1

import java.util.*;

import java.lang.*;

import java.util.Comparator;

public class Term implements Comparable<Term> {

  

public double weight;

public String query;

  

/*Initializes a term with the given query string and weight*/

public Term(String query, double w) {

//exception will be thrown if query word is null

if (query == null) {

throw new java.lang.NullPointerException();

}

//exception will be thrown if weight of the word is less than 0

if (w < 0) {

throw new java.lang.IllegalArgumentException();

}

this.weight = w; //Initialize weight

this.query = query; //Initialize query

}

  

/*Compares the two terms in descending order by weight*/

public static Comparator<Term> byReverseWeightOrder() {

return new Comparator<Term>() {

public int compare(Term x, Term y) {

if (x.weight > y.weight) {

return -1;

} else if (x.weight < y.weight) {

return 1;

} else {

return 0;

}

}

};

}

  

/*Compares the two terms in descending order but using only the first r characters

of each query.*/

public static Comparator<Term> byPrefixOrder(final int textLength) {

final int x = textLength;

return new Comparator<Term>() {

public int compare(Term term1, Term term2) {

String string1 = term1.query;

String string2 = term2.query;

  

  

//Find min length of either text input or the term

int minlength;

if (string1.length() < string2.length()) {

minlength = string1.length();

} else {

minlength = string2.length();

}

//Compare the substring of the larger string with the smaller string

//Returns -1 if the two strings lengths are equal, returns 1 else wise

if (minlength >= textLength) {

return string1.substring(0, x).compareToIgnoreCase(string2.substring(0, x));

} else if (string1.substring(0, minlength).compareToIgnoreCase(string2.substring(0, minlength)) == 0) {

if (string1.length() == minlength) {

return -1;

} else {

return 1;

}

} else {

return string1.substring(0, minlength).compareToIgnoreCase(string2.substring(0, minlength));

}

}

};

}

/*Compares the two terms in lexicographic order by query. */

public int compareTo(Term that) {

String x = this.query;

String y = that.query;

return x.compareToIgnoreCase(y); //Compares the two strings, ignoring the case

}

/*Returns a string representation of this term in the following format: the

weight, followed by a tab, followed by the query*/

public String toString() {

return Double.toString(this.weight) + "\t" + this.query;

}

public static void main(String[] args)

{

Term[] termArray = new Term[20];

for(int i = 0; i < 20; i++)

{

termArray[i] = new Term("Chegg"+i,i+(20*Math.random()));

}

  

for(int i = 0; i < 20; i++)

{

System.out.println(termArray[i]);

}

  

System.out.println();

  

Arrays.sort(termArray);

  

for(int i = 0; i < 20; i++)

{

System.out.println(termArray[i]);

}

  

System.out.println();

  

Arrays.sort(termArray, Term.byReverseWeightOrder());

  

for(int i = 0; i < 20; i++)

{

System.out.println(termArray[i]);

}

  

System.out.println();

  

Arrays.sort(termArray, Term.byPrefixOrder(2));

  

for(int i = 0; i < 20; i++)

{

System.out.println(termArray[i]);

}

}

}

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