Question

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 int firstIndexOf(Key[] a, Key key, Comparator comparator) /* Returns the index of the last key in a[] that equals the search key, or -1 if no such key. */ public static int lastIndexOf(Key[] a, Key key, Comparator 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().

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 all that equals the search key, or -1 if no such key. */ public static <Key> int first IndexOf(Key [] a, key key, comparator<Key> comparator) /* Returns the index of the last key in all that equals the search key, or -l if no such key. */ public static <Key> int lastIndexOf(Key [] a, key key, Comparator<Key> 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 first IndexOf() and lastIndexOf() methods should make at most 1 + [log2 M1 compares in the worst case, where N is the length of the array. In this context, a compare is one call to comparator.compare().

Answer 1

Working code implemented in Java and comments for better understanding:

Note: Below is the code for BinarySearchDeluxe.java . Here I have provided implementation for both firstIndexOf() and lastIndexOf(). It works fine for me. Just include the needed libraries it will work perfectly.

Code for BinarySearchDeluxe.java

import edu.princeton.cs.algs4.In;
import edu.princeton.cs.algs4.StdOut;
import edu.princeton.cs.algs4.StdIn;
import java.util.Arrays;
import java.util.Comparator;

// Implements binary search for clients that may want to know the index of
// either the first or last key in a (sorted) collection of keys.
public class BinarySearchDeluxe {
// The index of the first key in a[] that equals the search key,
// or -1 if no such key.
public static <Key> int firstIndexOf(Key[] a, Key key,
Comparator<Key> comparator) {
   if (a == null || key == null || comparator == null) {
       throw new java.lang.NullPointerException();
   }
   if (a.length == 0) {
       return -1;
   }
   int l = 0;
   int r = a.length - 1;
   int index = -1;
   while (l <= r) {
       int mid = l + (r - l)/2;
       if (comparator.compare(key, a[mid]) < 0) {
           r = mid - 1;
          
       } else if (comparator.compare(key, a[mid]) > 0) {
           l = mid + 1;
       } else {
       index = mid;
       r = mid - 1;
       }
   }
  
   return index;
  
}

// The index of the last key in a[] that equals the search key,
// or -1 if no such key.
public static <Key> int lastIndexOf(Key[] a, Key key,
Comparator<Key> comparator) {
   if (a == null || key == null || comparator == null) {
       throw new java.lang.NullPointerException();
   }
   if (a == null || a.length == 0) {
       return -1;
   }
   int l = 0;
   int r = a.length - 1;
   int index = -1;
   while (l <= r) {
       int mid = l + (r - l)/2;
       if (comparator.compare(key, a[mid]) < 0) {
           r = mid - 1;
       } else if (comparator.compare(key, a[mid]) > 0){
           l = mid + 1;
       } else {
       index = mid;
       l = mid + 1;
      
   }
  
  
}
return index;
}
  

// Test client. [DO NOT EDIT]
public static void main(String[] args) {
String filename = args[0];
String prefix = args[1];
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();
in.readChar();
String query = in.readLine();
terms[i] = new Term(query.trim(), weight);
}
Arrays.sort(terms);
Term term = new Term(prefix);
Comparator<Term> prefixOrder = Term.byPrefixOrder(prefix.length());
int i = BinarySearchDeluxe.firstIndexOf(terms, term, prefixOrder);
int j = BinarySearchDeluxe.lastIndexOf(terms, term, prefixOrder);
int count = i == -1 && j == -1 ? 0 : j - i + 1;
StdOut.println(count);
}
}

Code Screenshots:

import edu.princeton.cs.algs4.In; import edu.princeton.cs.algs4.Stdout; import edu.princeton.cs.algs4.StdIn; import java.util.Arrays; import java.util.Comparator; 5 7 8 9 // Implements binary search for clients that may want to know the index of // either the first or last key in a (sorted) collection of keys. public class BinarySearchDeluxe { // The index of the first key in a[] that equals the search key, // or -1 if no such key. public static <key> int firstIndexOf(Key[] a, key key, Comparator<key> comparator) { if (a == null || key == null || comparator == null) { throw new java.lang.NullPointerException(); if (a.length == 0) { return -1; int 1 = 0; int r = a.length - 1; int index = -1; while (i <= r) { int mid = 1 + (r - 1)/2; if (comparator.compare(key, a[mid]) r = mid - 1; ) { } else if (comparator.compare(key, a[mid]) > 0) { 1 = mid + 1; } else { index = mid; r = mid - 1; return index; // The index of the last key in a[] that equals the search key, // or -1 if no such key. public static <key> int lastIndexOf(Key[] a, key key, Comparator<key> comparator) { if (a == null || key == null | comparator == null) { throw new java.lang.NullPointerException(); if (a == null || a.length == 0) { return -1; int 1 = 0; int r = a.length - 1; int index = -1; while (1 int mid = 1 + (r - 1)/2; if (comparator.compare(key, a[mid)) < 0) { r = mid - 1; } else if (comparator.compare(key, a[mid]) > 0){ 1 = mid + 1; } else { index = mid;

1 = mid + 1; return index; 68 } // Test client. [DO NOT EDIT] public static void main(String[] args) { String filename = args[@]; String prefix = args[1]; 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(); in.readchar(); String query = in.readLine(); terms[i] = new Term(query.trim(), weight); Arrays.sort(terms); Term term = new Term(prefix); Comparator Term> prefixorder = Term.byPrefixOrder (prefix.length(); int i = BinarySearchDeluxe.firstIndexOf(terms, term, prefixorder); int j = BinarySearchDeluxe.lastIndexOf(terms, term, prefixOrder); int count = i == -1 && j == -1 ? @: j-i + 1; Stdout.println(count);

Hope it helps. Thank you.