Maximum Level Sum of a Binary Tree in C++

Suppose we have the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on. We have to return the smallest level X such that the sum of all the values of nodes at level X is maximal. So if the tree is like −

Then the output will be 2, The level 1 sum = 1, level 2 sum is 7 + 0 = 7, level 2 sum is 7 + (-8) = -1, so max is of level 2, so output is 2.

To solve this, we will follow these steps −

• level := 1, sum := value of r, ansLevel := level, ansSum := sum
• define a queue q, insert given node r into q
• while q is not empty
  • capacity := size of q
  • increase level by 1, sum := 0
  • while capacity is not 0
    • node := front node from q, delete node from q
    • if right of node is valid, then sum := sum + value of right node, insert right node into q
    • if left of node is valid, then sum := sum + value of left node, insert left node into q
    • decrease capacity by 1
  • if ansSum < sum, then ansSum := sum, ansLevel := level
• return ansLevel

Example(C++)

Let us see the following implementation to get a better understanding −

 Live Demo Live Demo

#include <bits/stdc++.h>
using namespace std;
class TreeNode{
   public:
      int val;
      TreeNode *left, *right;
      TreeNode(int data){
         val = data;
         left = NULL;
         right = NULL;
      }
};
void insert(TreeNode **root, int val){
   queue<TreeNode*> q;
   q.push(*root);
   while(q.size()){
      TreeNode *temp = q.front();
      q.pop();
      if(!temp->left){
         if(val != NULL)
            temp->left = new TreeNode(val);
         else
            temp->left = new TreeNode(0);
         return;
      }
      else{
         q.push(temp->left);
      }
      if(!temp->right){
         if(val != NULL)
            temp->right = new TreeNode(val);
         else
            temp->right = new TreeNode(0);
         return;
      }
      else{
         q.push(temp->right);
      }
   }
}
TreeNode *make_tree(vector<int> v){
   TreeNode *root = new TreeNode(v[0]);
   for(int i = 1; i<v.size(); i++){
      insert(&root, v[i]);
   }
   return root;
}
class Solution {
public:
   int maxLevelSum(TreeNode* r) {
      int level = 1, sum = r->val;
      int ansLevel = level, ansSum = sum;
      queue <TreeNode*> q;
      q.push(r);
      while(!q.empty()){
         int capacity = q.size();
         level++;
         sum = 0;
         while(capacity--){
            TreeNode* node = q.front();
            q.pop();
            if(node->right){
               sum += node->right->val;
               q.push(node->right);
            }
            if(node->left){
               sum += node->left->val;
               q.push(node->left);
            }
         }
         if(ansSum<sum){
            ansSum = sum;
            ansLevel = level;
         }
      }
      return ansLevel;
   }
};
main(){
   vector<int> v = {1,7,0,7,-8,NULL,NULL};
   TreeNode *root = make_tree(v);
   Solution ob;
   cout <<ob.maxLevelSum(root);
}

Input

[1,7,0,7,-8,null,null]

Output

2