Question

Modifying the tree traversal C program shown below to do reversed tree traversal as defined below.

Reversed PreOrder: Root, Right, Left.

Reversed InOrder:     Right, Root, Left.

Reversed PostOrder: Right, Left, Root.

The tree is:

Root = 1, Left(1) = -2, Right(1) = -3;

Left(-2) = 4, Right(-2) = 5;

Left(-3) = 6, Right(-3)= 7;

Left(5) = -8, Right(5)= -9;

Left(7) = 10, Right(7) = 11;

Left(11) = -12, Right(11) = -13;

Left(-13) = 14.

Your program should output the printed sequence of node IDs (positive or negative) according to the required order.

Code:

// C program for different tree traversals
#include <stdio.h>
#include <stdlib.h>

/* A binary tree node has data, pointer to left child
and a pointer to right child */
struct node
{
   int data;
   struct node* left;
   struct node* right;
};

/* Helper function that allocates a new node with the
given data and NULL left and right pointers. */
struct node* newNode(int data)
{
   struct node* node = (struct node*)
                               malloc(sizeof(struct node));
   node->data = data;
   node->left = NULL;
   node->right = NULL;

   return(node);
}

/* Given a binary tree, print its nodes according to the
"bottom-up" postorder traversal. */
void printPostorder(struct node* node)
{
   if (node == NULL)
       return;

   // first recur on left subtree
   printPostorder(node->left);

   // then recur on right subtree
   printPostorder(node->right);

   // now deal with the node
   printf("%d ", node->data);
}

/* Given a binary tree, print its nodes in inorder*/
void printInorder(struct node* node)
{
   if (node == NULL)
       return;

   /* first recur on left child */
   printInorder(node->left);

   /* then print the data of node */
   printf("%d ", node->data);

   /* now recur on right child */
   printInorder(node->right);
}

/* Given a binary tree, print its nodes in preorder*/
void printPreorder(struct node* node)
{
   if (node == NULL)
       return;

   /* first print data of node */
   printf("%d ", node->data);

   /* then recur on left sutree */
   printPreorder(node->left);

   /* now recur on right subtree */
   printPreorder(node->right);
}     

/* Driver program to test above functions*/
int main()
{
   struct node *root = newNode(1);
   root->left           = newNode(2);
   root->right       = newNode(3);
   root->left->left   = newNode(4);
   root->left->right = newNode(5);

   printf("\nPreorder traversal of binary tree is \n");
   printPreorder(root);

   printf("\nInorder traversal of binary tree is \n");
   printInorder(root);

   printf("\nPostorder traversal of binary tree is \n");
   printPostorder(root);

   getchar();
   return 0;
}

Answer 1

// C program for different tree traversals
#include <stdio.h>
#include <stdlib.h>

/* A binary tree node has data, pointer to left child
and a pointer to right child */
struct node
{
int data;
struct node* left;
struct node* right;
};

/* Helper function that allocates a new node with the
given data and NULL left and right pointers. */
struct node* newNode(int data)
{
struct node* node = (struct node*)
malloc(sizeof(struct node));
node->data = data;
node->left = NULL;
node->right = NULL;

return(node);
}

/* Given a binary tree, print its nodes according to the
"bottom-up" postorder traversal. */
void printPostorder(struct node* node)
{
if (node == NULL)
return;

//first recur on right subtree
printPostorder(node->right);

// then recur on left subtree
printPostorder(node->left);   

// now deal with the node
printf("%d ", node->data);
}

/* Given a binary tree, print its nodes in inorder*/
void printInorder(struct node* node)
{
if (node == NULL)
return;

/* first recur on right child */
printInorder(node->right);

/* then print the data of node */
printf("%d ", node->data);

/* now recur on left child */
printInorder(node->left);

}

/* Given a binary tree, print its nodes in preorder*/
void printPreorder(struct node* node)
{
if (node == NULL)
return;

/* first print data of node */
printf("%d ", node->data);

/* then recur on right subtree */
printPreorder(node->right);

/* now recur on left sutree */
printPreorder(node->left);

}   

/* Driver program to test above functions*/
int main()
{
struct node *root = newNode(1);
root->left = newNode(2);
root->right = newNode(3);
root->left->left = newNode(4);
root->left->right = newNode(5);

printf("\nPreorder traversal of binary tree is \n");
printPreorder(root);

printf("\nInorder traversal of binary tree is \n");
printInorder(root);

printf("\nPostorder traversal of binary tree is \n");
printPostorder(root);

getchar();
return 0;
}

OUTPUT: