Question

Recursion java:

1. Write a recursive algorithm to add all the elements of an array of n elements

2. Write a recursive algorithm to get the minimum element of an array of n elements

3. Write a recursive algorithm to add the corresponding elements of two arrays (A and B) of n elements. Store the results in a third array C

.4. Write a recursive algorithm to get the maximum element of a binary tree

5. Write a recursive algorithm to get the number of elements of a binary tree

Answer 1

1. Recursive algorithm to add elements of an array:

// ArraySum.java
import java.util.Scanner;
public class ArraySum
{
    static int findSum(int array[], int n){
        if(n<=0)
            return 0;
        return (findSum(array, n-1) + array[n-1]);
    }
        public static void main(String[] args) {
            System.out.println("Enter number of elements: ");
            Scanner sc = new Scanner(System.in);
            int n = sc.nextInt();
            int array[] = new int[n];
            System.out.println("Enter elements:");
            for(int i=0; i<n; i++)
                array[i] = sc.nextInt();
           int sum = findSum(array, n);
            System.out.println("Sum of array elements: " + sum);
        }
}

Output:

Enter number of elements:                                      
5                                                              
Enter elements:                                                
1 2 3 4 5                                                         
Sum of array elements: 15

2. Recursive algorithm to get the minimum element of an array:

// ArrayMinimum.java
import java.util.Scanner;
public class ArrayMinimum
{
    static int findMin(int array[], int n){
        if(n==1)
            return array[0];
        return Math.min(array[n-1], findMin(array, n-1));
    }
        public static void main(String[] args) {
            System.out.println("Enter number of elements: ");
            Scanner sc = new Scanner(System.in);
            int n = sc.nextInt();
            int array[] = new int[n];
            System.out.println("Enter elements:");
            for(int i=0; i<n; i++)
                array[i] = sc.nextInt();
           int min = findMin(array, n);
            System.out.println("Min of array elements: " + min);
        }
}

Output:

Enter number of elements:                                      
3                                                              
Enter elements:                                                
22 -30 10                                                            
Min of array elements: -30  

3. Recursive algorithm to add the corresponding elements of two arrays and store them in third array.

// ArraySum.java
import java.util.Scanner;
public class ArraySum
{
    static int[] findSum(int[] A, int[] B, int[] C, int n){
        if(n<=0)
            return C;
        C[n-1] = A[n-1] + B[n-1];
        return findSum(A, B, C, n-1);
    }
        public static void main(String[] args) {
            System.out.println("Enter number of elements: ");
            Scanner sc = new Scanner(System.in);
            int n = sc.nextInt();
            int A[] = new int[n];
            int B[] = new int[n];
            System.out.println("Enter elements of first array:");
            for(int i=0; i<n; i++)
                A[i] = sc.nextInt();
            System.out.println("Enter elements of second array:");
            for(int i=0; i<n; i++)
                B[i] = sc.nextInt();
            int C[] = new int[n];
            findSum(A, B, C, n);
            System.out.println("Sum Array:");
            for(int i=0; i<n; i++)
                System.out.print(C[i] + " ");
        }
}

Output:

Enter number of elements:                                                                                                     
5                                                                                                                             
Enter elements of first array:                                                                                                
1 2 3 4 5                                                                                                                     
Enter elements of second array:                                                                                               
1 2 3 4 5                                                                                                                     
Sum Array:                                                                                                                    
2 4 6 8 10

4. Recursive program to find the minimum element of binary tree.

// BinaryTreeMaximum.java
class Node{
    int data;
    Node left, right;
    public Node(int data){
        this.data = data;
        left = right = null;
    }
}
class BinaryTree{
    Node root;
    static int findMax(Node node){
        if(node == null)
            return Integer.MIN_VALUE;
        int res = node.data;
        int l = findMax(node.left);
        int r = findMax(node.right);
        if(l>r)
            res = l;
        if(r>res)
            res = r;
        return res;
    }
}
public class BinaryTreeMaximum
{
        public static void main(String[] args) {
            BinaryTree t = new BinaryTree();
            t.root = new Node(10);
            t.root.left = new Node(25);
            t.root.right = new Node(30);
            t.root.left.left = new Node(50);
            t.root.left.right = new Node(45);
            System.out.println("Maximum element in binary tree: " + t.findMax(t.root));
        }
}

Output:

Maximum element in binary tree: 50

5. Recursive program to find the number of elements in binary tree.

// BinaryTreeElements.java
class Node{
    int data;
    Node left, right;
    public Node(int data){
        this.data = data;
        left = right = null;
    }
}
class BinaryTree{
    Node root;
    int size(){
        return size(root);
    }
    int size(Node node){
        if(node == null)
            return 0;
        else
            return (size(node.left) + 1 + size(node.right));
    }
}
public class BinaryTreeElements
{
        public static void main(String[] args) {
            BinaryTree t = new BinaryTree();
            t.root = new Node(10);
            t.root.left = new Node(25);
            t.root.right = new Node(30);
            t.root.left.left = new Node(50);
            t.root.left.right = new Node(45);
            System.out.println("Number of elements in binary tree: " + t.size());
        }
}

Output:

Number of elements in binary tree: 5

Note: If reader wants to copy and use the code provided in the answer, the reader has to make sure to replace [NBSP] with spaces, if found any in the code. Else the program may not compile/run successfully.