⭐ Must Read: web//https://www.geeksforgeeks.org/check if leaf traversal of two binary trees is same

Leaf traversal is sequence of leaves traversed from left to right. The problem is to check if leaf traversals of two given Binary Trees are same or not.
Expected time complexity O(n). Expected auxiliary space O(h1 + h2) where h1 and h2 are heights of two Binary Trees.

Examples:

Input: Roots of below Binary Trees
         1            
        / \
       2   3      
      /   / \          
     4   6   7

          0
        /   \
       5     8      
        \   / \        
        4   6  7
Output: same
Leaf order traversal of both trees is 4 6 7     

Input: Roots of below Binary Trees
         0            
        / \
       1   2       
      / \       
     8   9   

         1
        / \
       4   3     
        \ / \        
        8 2  9

Output: Not Same
Leaf traversals of two trees are different.
For first, it is 8 9 2 and for second it is
8 2 9

We strongly recommend you to minimize your browser and try this yourself first.
A Simple Solution is traverse first tree and store leaves from left and right in an array. Then traverse other tree and store leaves in another array. Finally compare two arrays. If both arrays are same, then return true.
The above solution requires O(m+n) extra space where m and n are nodes in first and second tree respectively.
How to check with O(h1 + h2) space?
The idea is use iterative traversal. Traverse both trees simultaneously, look for a leaf node in both trees and compare the found leaves. All leaves must match.

Algorithm:

1. Create empty stacks stack1 and stack2 
   for iterative traversals of tree1 and tree2

2. insert (root of tree1) in stack1
   insert (root of tree2) in stack2

3. Stores current leaf nodes of tree1 and tree2
temp1 = (root of tree1) 
temp2 = (root of tree2)  

4. Traverse both trees using stacks
while (stack1 and stack2 parent empty) 
{
    // Means excess leaves in one tree
    if (if one of the stacks are empty)   
    return false

   // get next leaf node in tree1 
   temp1 = stack1.pop()
   while (temp1 is not leaf node) 
   {
        push right child to stack1     
    push left child to stack1
   }

   // get next leaf node in tree2     
   temp2 = stack2.pop()
   while (temp2 is not leaf node) 
   {
        push right child to stack2      
    push left child to stack2
   }

   // If leaves do not match return false
   if (temp1 != temp2)                  
       return false
}

5. If all leaves matched, return true

Below is Java implementation of the above algorithm.

C++

// C++ code to check if leaf traversals 
// of two Binary Trees are same or not. 
#include <bits/stdc++.h> 
using namespace std; 
  
// Binary Tree Node 
struct Node { 
    int data; 
    Node* left; 
    Node* right; 
}; 
  
// Returns new Node with data as 
// input to below function. 
Node* newNode(int d) 
{ 
    Node* temp = new Node; 
    temp->data = d; 
    temp->left = NULL; 
    temp->right = NULL; 
  
    return temp; 
} 
  
// checks if a given node is leaf or not. 
bool isLeaf(Node* root) 
{ 
    if (root == NULL) 
        return false; 
    if (!root->left && !root->right) 
        return true; 
    return false; 
} 
  
// iterative function. 
// returns true if leaf traversals 
// are same, else false. 
bool isSame(Node* root1, Node* root2) 
{ 
    stack<Node*> s1; 
    stack<Node*> s2; 
  
    // push root1 to empty stack s1. 
    s1.push(root1); 
  
    // push root2 to empty stack s2. 
    s2.push(root2); 
  
    // loop until either of stacks are non-empty. 
    while (!s1.empty() || !s2.empty())  
    { 
        // this means one of the stacks has 
        // extra leaves, hence return false. 
        if (s1.empty() || s2.empty()) 
            return false; 
  
        Node* temp1 = s1.top(); 
        s1.pop(); 
        while (temp1 != NULL && !isLeaf(temp1)) 
        { 
            // Push right child if exists 
            if (temp1->right) 
                s1.push(temp1->right); 
  
            // Push left child if exists 
            if (temp1->left) 
                s1.push(temp1->left); 
  
            // Note that right child(if exists) 
            // is pushed before left child(if exists). 
            temp1 = s1.top(); 
            s1.pop(); 
        } 
  
        Node* temp2 = s2.top(); 
        s2.pop(); 
        while (temp2 != NULL && !isLeaf(temp2))  
        { 
            // Push right child if exists 
            if (temp2->right) 
                s2.push(temp2->right); 
  
            // Push left child if exists 
            if (temp2->left) 
                s2.push(temp2->left); 
            temp2 = s2.top(); 
            s2.pop(); 
        } 
  
        if (!temp1 && temp2) 
            return false; 
        if (temp1 && !temp2) 
            return false; 
        if (temp1 && temp2) { 
            return temp1->data == temp2->data; 
        } 
    } 
  
    // all leaves are matched 
    return true; 
} 
  
// Driver Code 
int main() 
{ 
    Node* root1 = newNode(1); 
    root1->left = newNode(2); 
    root1->right = newNode(3); 
    root1->left->left = newNode(4); 
    root1->right->left = newNode(6); 
    root1->right->right = newNode(7); 
  
    Node* root2 = newNode(0); 
    root2->left = newNode(1); 
    root2->right = newNode(5); 
    root2->left->right = newNode(4); 
    root2->right->left = newNode(6); 
    root2->right->right = newNode(7); 
  
    if (isSame(root1, root2)) 
        cout << "Same"; 
    else
        cout << "Not Same"; 
    return 0; 
} 
  
// This code is contributed 
// by AASTHA VARMA

Java

// Java program to check if two Leaf Traversal of 
// Two Binary Trees is same or not 
import java.util.*; 
import java.lang.*; 
import java.io.*; 
  
// Binary Tree node 
class Node  
{ 
    int data; 
    Node left, right; 
    public Node(int x) 
    { 
        data = x; 
        left = right = null; 
    } 
    public boolean isLeaf() 
    { 
        return (left == null && right == null); 
    } 
} 
  
class LeafOrderTraversal 
{ 
    // Returns true of leaf traversal of two trees is 
    // same, else false 
    public static boolean isSame(Node root1, Node root2) 
    { 
        // Create empty stacks.  These stacks are going 
        // to be used for iterative traversals. 
        Stack<Node> s1 = new Stack<Node>(); 
        Stack<Node> s2 = new Stack<Node>(); 
  
        s1.push(root1); 
        s2.push(root2); 
  
        // Loop until either of two stacks is not empty 
        while (!s1.empty() || !s2.empty()) 
        { 
            // If one of the stacks is empty means other 
            // stack has extra leaves so return false 
            if (s1.empty() || s2.empty()) 
                return false; 
  
            Node temp1 = s1.pop(); 
            while (temp1 != null && !temp1.isLeaf())  
            { 
                // Push right and left children of temp1. 
                // Note that right child is inserted 
                // before left 
                if (temp1.right != null) 
                    s1.push(temp1.right); 
                if (temp1.left != null) 
                    s1.push(temp1.left); 
                temp1 = s1.pop(); 
            } 
  
            // same for tree2 
            Node temp2 = s2.pop(); 
            while (temp2 != null && !temp2.isLeaf())  
            { 
                if (temp2.right != null) 
                    s2.push(temp2.right); 
                if (temp2.left != null) 
                    s2.push(temp2.left); 
                temp2 = s2.pop(); 
            } 
  
            // If one is null and other is not, then 
            // return false 
            if (temp1 == null && temp2 != null) 
                return false; 
            if (temp1 != null && temp2 == null) 
                return false; 
  
            // If both are not null and data is not 
            // same return false 
            if (temp1 != null && temp2 != null)  
            { 
                if (temp1.data != temp2.data) 
                    return false; 
            } 
        } 
  
        // If control reaches this point, all leaves 
        // are matched 
        return true; 
    } 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Let us create trees in above example 1 
        Node root1 = new Node(1); 
        root1.left = new Node(2); 
        root1.right = new Node(3); 
        root1.left.left = new Node(4); 
        root1.right.left = new Node(6); 
        root1.right.right = new Node(7); 
  
        Node root2 = new Node(0); 
        root2.left = new Node(1); 
        root2.right = new Node(5); 
        root2.left.right = new Node(4); 
        root2.right.left = new Node(6); 
        root2.right.right = new Node(7); 
  
        if (isSame(root1, root2)) 
            System.out.println("Same"); 
        else
            System.out.println("Not Same"); 
    } 
}

Python3

# Python3 program to check if two Leaf 
# Traversal of Two Binary Trees is same or not 
  
# Binary Tree node 
  
  
class Node: 
    def __init__(self, x): 
        self.data = x 
        self.left = self.right = None
  
    def isLeaf(self): 
        return (self.left == None and
                self.right == None) 
  
# Returns true of leaf traversal of 
# two trees is same, else false 
  
  
def isSame(root1, root2): 
  
    # Create empty stacks. These stacks are going 
    # to be used for iterative traversals. 
    s1 = [] 
    s2 = [] 
  
    s1.append(root1) 
    s2.append(root2) 
  
    # Loop until either of two stacks 
    # is not empty 
    while (len(s1) != 0 or len(s2) != 0): 
  
        # If one of the stacks is empty means other 
        # stack has extra leaves so return false 
        if (len(s1) == 0 or len(s2) == 0): 
            return False
  
        temp1 = s1.pop(-1) 
        while (temp1 != None and not temp1.isLeaf()): 
  
            # append right and left children of temp1. 
            # Note that right child is inserted 
            # before left 
            if (temp1.right != None): 
                s1.append(temp1. right) 
            if (temp1.left != None): 
                s1.append(temp1.left) 
                temp1 = s1.pop(-1) 
  
        # same for tree2 
        temp2 = s2.pop(-1) 
        while (temp2 != None and not temp2.isLeaf()): 
            if (temp2.right != None): 
                s2.append(temp2.right) 
            if (temp2.left != None): 
                s2.append(temp2.left) 
            temp2 = s2.pop(-1) 
  
        # If one is None and other is not, 
        # then return false 
        if (temp1 == None and temp2 != None): 
            return False
        if (temp1 != None and temp2 == None): 
            return False
  
        # If both are not None and data is 
        # not same return false 
        if (temp1 != None and temp2 != None): 
            if (temp1.data != temp2.data): 
                return False
  
    # If control reaches this point, 
    # all leaves are matched 
    return True
  
  
# Driver Code 
if __name__ == '__main__': 
  
    # Let us create trees in above example 1 
    root1 = Node(1) 
    root1.left = Node(2) 
    root1.right = Node(3) 
    root1.left.left = Node(4) 
    root1.right.left = Node(6) 
    root1.right.right = Node(7) 
  
    root2 = Node(0) 
    root2.left = Node(1) 
    root2.right = Node(5) 
    root2.left.right = Node(4) 
    root2.right.left = Node(6) 
    root2.right.right = Node(7) 
  
    if (isSame(root1, root2)): 
        print("Same") 
    else: 
        print("Not Same") 
  
# This code is contributed by pranchalK 

C#

// C# program to check if two Leaf Traversal 
// of Two Binary Trees is same or not 
using System; 
using System.Collections.Generic; 
  
// Binary Tree node 
public class Node { 
    public int data; 
    public Node left, right; 
    public Node(int x) 
    { 
        data = x; 
        left = right = null; 
    } 
    public virtual bool Leaf 
    { 
        get {  
          return (left == null && right == null);  
        } 
    } 
} 
  
class GFG { 
    // Returns true of leaf traversal of 
    // two trees is same, else false 
    public static bool isSame(Node root1, Node root2) 
    { 
        // Create empty stacks. These stacks 
        // are going to be used for iterative 
        // traversals. 
        Stack<Node> s1 = new Stack<Node>(); 
        Stack<Node> s2 = new Stack<Node>(); 
  
        s1.Push(root1); 
        s2.Push(root2); 
  
        // Loop until either of two stacks 
        // is not empty 
        while (s1.Count > 0 || s2.Count > 0) 
        { 
            // If one of the stacks is empty means other 
            // stack has extra leaves so return false 
            if (s1.Count == 0 || s2.Count == 0) 
            { 
                return false; 
            } 
  
            Node temp1 = s1.Pop(); 
            while (temp1 != null && !temp1.Leaf)  
            { 
                // Push right and left children of temp1. 
                // Note that right child is inserted 
                // before left 
                if (temp1.right != null)  
                { 
                    s1.Push(temp1.right); 
                } 
                if (temp1.left != null)  
                { 
                    s1.Push(temp1.left); 
                } 
                temp1 = s1.Pop(); 
            } 
  
            // same for tree2 
            Node temp2 = s2.Pop(); 
            while (temp2 != null && !temp2.Leaf)  
            { 
                if (temp2.right != null)  
                { 
                    s2.Push(temp2.right); 
                } 
                if (temp2.left != null)  
                { 
                    s2.Push(temp2.left); 
                } 
                temp2 = s2.Pop(); 
            } 
  
            // If one is null and other is not, 
            // then return false 
            if (temp1 == null && temp2 != null)  
            { 
                return false; 
            } 
            if (temp1 != null && temp2 == null)  
            { 
                return false; 
            } 
  
            // If both are not null and data 
            // is not same return false 
            if (temp1 != null && temp2 != null)  
            { 
                if (temp1.data != temp2.data)  
                { 
                    return false; 
                } 
            } 
        } 
  
        // If control reaches this point, 
        // all leaves are matched 
        return true; 
    } 
  
    // Driver Code 
    public static void Main(string[] args) 
    { 
        // Let us create trees in above example 1 
        Node root1 = new Node(1); 
        root1.left = new Node(2); 
        root1.right = new Node(3); 
        root1.left.left = new Node(4); 
        root1.right.left = new Node(6); 
        root1.right.right = new Node(7); 
  
        Node root2 = new Node(0); 
        root2.left = new Node(1); 
        root2.right = new Node(5); 
        root2.left.right = new Node(4); 
        root2.right.left = new Node(6); 
        root2.right.right = new Node(7); 
  
        if (isSame(root1, root2)) { 
            Console.WriteLine("Same"); 
        } 
        else { 
            Console.WriteLine("Not Same"); 
        } 
    } 
} 
  
// This code is contributed by Shrikant13

Output

Same

This article is contributed by Kumar Gaurav. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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Check if leaf traversal of two Binary Trees is same?

C++

Java

Python3

C#

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