Print all leaf nodes of a binary tree from right to left in C++

In this problem, we are given a binary tree and we have to print all leaf nodes of the binary tree from right to left.

Let’s take an example to understand the problem

Input −

Output − 7 4 1

To solve this problem, we will have to traverse the binary tree. This traversal can be done in two ways −

Preorder traversal − This traversal uses recursion. Here, we will traverse, root then left and then right subtree. If we encounter a leaf node then we will print it, else we check for children of the node and explore them to find leaf node.

Example

Program to show the implementation of our solution −

 Live Demo

#include <iostream>
using namespace std;
struct Node {
   int data;
   struct Node *left, *right;
};
Node* insertNode(int data) {
   Node* temp = new Node;
   temp->data = data;
   temp->left = temp->right = NULL;
   return temp;
}
void findLeafNode(Node* root) {
   if (!root)
      return;
   if (!root->left && !root->right) {
      cout<<root->data<<"\t";
      return;
   }
   if (root->right)
      findLeafNode(root->right);
   if (root->left)
      findLeafNode(root->left);
}
int main() {
   Node* root = insertNode(21);
   root->left = insertNode(5);
   root->right = insertNode(11);
   root->left->left = insertNode(8);
   root->left->right = insertNode(98);
   root->right->left = insertNode(2);
   root->right->right = insertNode(8);
   cout<<"Leaf nodes of the tree from right to left are:\n";
   findLeafNode(root);
   return 0;
}

Output

Leaf nodes of the tree from right to left are −
18 2 98 8

Postorder Traversal − This traversal to find the leaf node will use iteration. We will use a stack to store data and traverse the tree in a postorder manner (first right subtree then left subtree and then root) and print leaf nodes.

Example

Program to show the implementation of our solution −

 Live Demo

#include<bits/stdc++.h>
using namespace std;
struct Node {
   Node* left;
   Node* right;
   int data;
};
Node* insertNode(int key) {
   Node* node = new Node();
   node->left = node->right = NULL;
   node->data = key;
   return node;
}
void findLeafNode(Node* tree) {
   stack<Node*> treeStack;
   while (1) {
      if (tree) {
         treeStack.push(tree);
         tree = tree->right;
      } else {
         if (treeStack.empty())
            break;
         else {
            if (treeStack.top()->left == NULL) {
               tree = treeStack.top();
               treeStack.pop();
               if (tree->right == NULL)
                  cout<<tree->data<<"\t";
            }
            while (tree == treeStack.top()->left) {
               tree = treeStack.top();
               treeStack.pop();
               if (treeStack.empty())
                  break;
            }
            if (!treeStack.empty())
               tree = treeStack.top()->left;
            else
               tree = NULL;
         }  
      }
   }
}
int main(){
   Node* root = insertNode(21);
   root->left = insertNode(5);
   root->right = insertNode(11);
   root->left->left = insertNode(8);
   root->left->right = insertNode(98);
   root->right->left = insertNode(2);
   root->right->right = insertNode(18);
   cout<<"Leaf nodes of the tree from right to left are:\n";
   findLeafNode(root);
   return 0;
}

Output

Leaf nodes of the tree from right to left are −
18 2 98 8