Question

Complete the recursive method binarySearch() with the following specifications:

import java.util.ArrayList;

public class BinarySearchLab {

public static int binarySearch(int target, ArrayList list, int lower, int upper) {
// Your code here
}

public static void main(String[] args) {
// Helper function to read an ArrayList from input
ArrayList myList = readArrayList();

// Example usage:
int target = 42;
int result = binarySearch(target, myList, 0, myList.size() - 1);
System.out.println("Index of " + target + ": " + result);
}

// Helper function to read an ArrayList from input
public static ArrayList readArrayList() {
// Implementation details not provided
// Assume the function reads an ArrayList from input and returns it
return null;
}
}

Answer 1

The given code implements the binary search algorithm recursively. It searches for a target value in an ArrayList by dividing the list into halves at each step.

Step-by-step explanation:

The given code is for implementing the binary search algorithm recursively. The binarySearch() method takes four parameters - the target value to be searched, the list to be searched in, the lower bound of the search range, and the upper bound of the search range.

To implement the binary search algorithm recursively, we perform the following steps:

1. Check if the lower bound is greater than the upper bound. If it is, then the target value is not found in the list and we return -1.
2. Calculate the middle index of the search range by taking the average of the lower and upper bounds.
3. Compare the middle element of the list with the target value. If they are equal, we have found the target and return the index of the middle element.
4. If the target value is less than the middle element, recursively call the binarySearch() method on the lower half of the range.
5. If the target value is greater than the middle element, recursively call the binarySearch() method on the upper half of the range.

By following these steps, the binarySearch() method performs a binary search and returns the index of the target value in the list, or -1 if it is not found.