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Ace the AP Computer Science Exam for High Schoolers

Solution Review: Recursive Binary Search

Explore the recursive binary search algorithm through detailed explanation and code examples in Java. Understand how base and recursive cases work together to locate values in arrays, and learn how to adjust search boundaries using left and right pointers for efficient searching.

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Rubric criteria

Solution

Java
class BinarySearch
{
    public static int search(int[] array, int left, int right, int value)
    {
        if(right >= left)
        {
            int middle = (left + right)/2;
            if (array[middle] == value)     // second base case
                return middle;
            else if(array[middle] > value)  // first recursive case
                return search(array, left, middle-1, value);
            else                            // second recursive case
                return search(array, middle+1, right, value);
        }
        else                               // first base case
            return -1;
    }
    public static int binarySearch(int[]array, int value)
    {
        return search(array, 0, array.length-1, value);    // calling recursive method
    }
    public static void main(String args[]) 
    {
        int[] array = {1, 2, 3, 4, 5, 6};
        System.out.println( binarySearch(array, 5) );
    }
}

Rubric-wise explanation

According to the problem statement, a call from the main function will send the array and a value that is to be found. Look at line 22. We create the header of a binarySearch() function. It takes array and value as input and returns the position of value in array. In this function, we call another method: search.

Point 1:

The search method is a recursive method. To carry out the recursion ...