Sum of child nodes

Problem

In a binary tree change each node's value(except leaf node) as the sum of left and right subtree's value.

            Constructed binary tree is:
                    1
                 /      \
                2        3
              /  \        \
             4   5        8
                        /    \
                       6       7


          After sum stored is in each node, binary tree is:
                   35
                 /    \
                9     21
              /  \       \
             4   5       13
                        /   \
                       6     7


        

Solution

In a recursive function we return the sum of the subtree rooted at a particular node and change the value of the node also. If the node is null return 0, otherwise it calls it recursively to its left and right children. It returns this node’s value plus the results returned by calling the function on its left and right children. And sets the value of the current node to the sum of the left and right side.

Code

/*
 * In a binary tree change each node's value(except leaf node) 
 * as the sum of left and right subtree's value. 
 *  
   Constructed binary tree is:
           1
        /      \
       2        3
     /  \        \
    4   5        8
               /    \
              6       7
  

 After sum stored is in each node, binary tree is:
          35
        /    \
       9     21
     /  \       \
    4   5       13
               /   \
              6     7
  
 */
public class BinaryTreeSumChildNodes
{

 /**
  * @param args
  */
 public static void main(String[] args)
 {

  Node a = new Node(1);
  Node b = new Node(2);
  Node c = new Node(3);
  Node d = new Node(4);
  Node e = new Node(5);
  Node f = new Node(8);
  Node g = new Node(6);
  Node h = new Node(7);
  a.left = b;
  a.right = c;
  b.left = d;
  b.right = e;
  c.right = f;
  f.left = g;
  f.right = h;
  printNice(a);
  System.out.println();
  makeSum(a);
  printNice(a);
 }

 public static int makeSum(Node root)
 {
  if (root == null)
   return 0;
  int temp = root.value;
  int sum = makeSum(root.left) + makeSum(root.right);
  if (root.left != null || root.right != null)
   root.value = sum;
  return temp + sum;
 }

 public static void printNice(Node root)
 {
  if (root == null)
   return;
  else
  {
   System.out.print(root.value);
   if (root.left != null)
   {
    System.out.print("L->[");
    printNice(root.left);
    System.out.print("]");
   }
   if (root.right != null)
   {
    System.out.print("R->[");
    printNice(root.right);
    System.out.print("]");
   }
  }
 }
}