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Sum of nodes at maximum depth of a Binary Tree | Iterative Approach
  • Difficulty Level : Easy
  • Last Updated : 11 Dec, 2020
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Given a root node to a tree, find the sum of all the leaf nodes which are at maximum depth from the root node.
Example: 

      1
    /   \
   2     3
  / \   / \
 4   5 6   7

Input : root(of above tree)
Output : 22

Explanation:
Nodes at maximum depth are 4, 5, 6, 7. 
So, the sum of these nodes = 22

Approach: There exists a recursive approach to this problem. This can also be solved using level order traversal and map. The idea is to do a traversal using a queue and keep track of the current level. A map has been used to store the sum of nodes at the current level. Once all nodes are visited and the traversal is done, the last element of the map will contain the sum at the maximum depth of the tree. 
Below is the implementation of the above approach: 
 

C++




// C++ program to calculate the sum of
// nodes at the maximum depth of a binary tree
#include <bits/stdc++.h>
using namespace std;
 
struct node {
    int data;
    node *left, *right;
} * temp;
 
node* newNode(int data)
{
    temp = new node;
    temp->data = data;
    temp->left = temp->right = NULL;
 
    return temp;
}
 
// Function to return the sum
int SumAtMaxLevel(node* root)
{
    // Map to store level wise sum.
    map<int, int> mp;
 
    // Queue for performing Level Order Traversal.
    // First entry is the node and
    // second entry is the level of this node.
    queue<pair<node*, int> > q;
 
    // Root has level 0.
    q.push({ root, 0 });
 
    while (!q.empty()) {
 
        // Get the node from front of Queue.
        pair<node*, int> temp = q.front();
        q.pop();
 
        // Get the depth of current node.
        int depth = temp.second;
 
        // Add the value of this node in map.
        mp[depth] += (temp.first)->data;
 
        // Push children of this node,
        // with increasing the depth.
        if (temp.first->left)
            q.push({ temp.first->left, depth + 1 });
 
        if (temp.first->right)
            q.push({ temp.first->right, depth + 1 });
    }
 
    map<int, int>::iterator it;
 
    // Get the max depth from map.
    it = mp.end();
 
    // last element
    it--;
 
    // return the max Depth sum.
    return it->second;
}
 
// Driver Code
int main()
{
    node* root = newNode(1);
    root->left = newNode(2);
    root->right = newNode(3);
    root->left->left = newNode(4);
    root->left->right = newNode(5);
    root->right->left = newNode(6);
    root->right->right = newNode(7);
 
    cout << SumAtMaxLevel(root) << endl;
    return 0;
}

Java




// Java program to calculate
// the sum of nodes at the
// maximum depth of a binary tree
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Queue;
 
class GFG{
     
static class Node
{
  int data;
  Node left, right;
  public Node(int data)
  {
    this.data = data;
    this.left = this.right =
                null;
  }
}
 
static class Pair
{
  Node node;
  int data;
  public Pair(Node node,
              int data)
  {
    this.node = node;
    this.data = data;
  }
}
 
// Function to return the sum
static int SumAtMaxLevel(Node root)
{
  // Map to store level wise sum.
  HashMap<Integer,
          Integer> mp = new HashMap<>();
 
  // Queue for performing Level
  // Order Traversal. First entry
  // is the node and second entry
  // is the level of this node.
  Queue<Pair> q = new LinkedList<>();
 
  // Root has level 0.
  q.add(new Pair(root, 0));
 
  while (!q.isEmpty())
  {
    // Get the node from
    // front of Queue.
    Pair temp = q.poll();
 
    // Get the depth of
    // current node.
    int depth = temp.data;
 
    // Add the value of this
    // node in map.
    if (!mp.containsKey(depth))
      mp.put(depth, 0);
    mp.put(depth, mp.get(depth) +
           temp.node.data);
 
    // Push children of this node,
    // with increasing the depth.
    if (temp.node.left != null)
      q.add(new Pair(temp.node.left,
                     depth + 1));
 
    if (temp.node.right != null)
      q.add(new Pair(temp.node.right,
                     depth + 1));
  }
 
  Object[] values = mp.values().toArray();
  return (int) values[values.length - 1];
}
 
// Driver Code
public static void main(String[] args)
{
  Node root = new Node(1);
  root.left = new Node(2);
  root.right = new Node(3);
  root.left.left = new Node(4);
  root.left.right = new Node(5);
  root.right.left = new Node(6);
  root.right.right = new Node(7);
 
  System.out.println(SumAtMaxLevel(root));
}     
}
 
// This code is contributed by sanjeev2552

Python3




# Python3 program to calculate the
# sum of nodes at the maximum depth
# of a binary tree
 
# Helper function that allocates a
# new node with the given data and
# None left and right poers.                                    
class newNode:
 
    # Constructor to create a new node
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None
 
# Function to return the sum
def SumAtMaxLevel(root):
 
    # Map to store level wise sum.
    mp = {}
 
    # Queue for performing Level Order
    # Traversal. First entry is the node
    # and second entry is the level of
    # this node.
    q = []
 
    # Root has level 0.
    q.append([root, 0])
 
    while (len(q)):
 
        # Get the node from front
        # of Queue.
        temp = q[0]
        q.pop(0)
 
        # Get the depth of current node.
        depth = temp[1]
 
        # Add the value of this node in map.
        if depth not in mp:
            mp[depth] = 0
        mp[depth] += (temp[0]).data
 
        # append children of this node,
        # with increasing the depth.
        if (temp[0].left) :
            q.append([temp[0].left,
                        depth + 1])
 
        if (temp[0].right) :
            q.append([temp[0].right,
                         depth + 1])
 
    # return the max Depth sum.
    return list(mp.values())[-1]
         
# Driver Code
if __name__ == '__main__':
     
    # Let us construct the Tree
    # shown in the above figure
    root = newNode(1)
    root.left = newNode(2)
    root.right = newNode(3)
    root.left.left = newNode(4)
    root.left.right = newNode(5)
    root.right.left = newNode(6)
    root.right.right = newNode(7)
    print(SumAtMaxLevel(root))
 
# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

C#




// C# program to calculate
// the sum of nodes at the
// maximum depth of a binary tree
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
  
class GFG{
      
class Node
{
  public int data;
public Node left, right;
  public Node(int data)
  {
    this.data = data;
    this.left = this.right =
                null;
  }
}
  
class Pair
{
  public Node node;
  public int data;
  public Pair(Node node,
              int data)
  {
    this.node = node;
    this.data = data;
  }
}
  
// Function to return the sum
static int SumAtMaxLevel(Node root)
{
  // Map to store level wise sum.
  Dictionary<int,int> mp = new Dictionary<int,int>();
  
  // Queue for performing Level
  // Order Traversal. First entry
  // is the node and second entry
  // is the level of this node.
  Queue q = new Queue();
  
  // Root has level 0.
  q.Enqueue(new Pair(root, 0));
  
  while (q.Count != 0)
  {
    // Get the node from
    // front of Queue.
    Pair temp = (Pair)q.Dequeue();
  
    // Get the depth of
    // current node.
    int depth = temp.data;
  
    // Add the value of this
    // node in map.
    if (!mp.ContainsKey(depth))
      mp[depth]= 0;
       
    mp[depth] = mp[depth]+temp.node.data;
  
    // Push children of this node,
    // with increasing the depth.
    if (temp.node.left != null)
      q.Enqueue(new Pair(temp.node.left,
                     depth + 1));
  
    if (temp.node.right != null)
      q.Enqueue(new Pair(temp.node.right,
                     depth + 1));
  }
  
  return mp.Values.Last();
}
  
// Driver Code
public static void Main(string[] args)
{
  Node root = new Node(1);
  root.left = new Node(2);
  root.right = new Node(3);
  root.left.left = new Node(4);
  root.left.right = new Node(5);
  root.right.left = new Node(6);
  root.right.right = new Node(7);
  
  Console.WriteLine(SumAtMaxLevel(root));
}     
}
 
// This code is contributed by rutvik_56
Output: 
22

 

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