# Subtree with Maximum Value - Facebook Top Interview Questions

### Problem Statement :

```Given a binary tree root, return the maximum sum of a subtree.

A subtree is defined to be some node in root including all of its descendants.

A subtree sum is the sum of all the node values in the subtree.

A subtree can be null in which case its sum is 0.

Constraints

1 ≤ n ≤ 100,000 where n is the number of nodes in root

Example 1

Input

root = [3, [0, null, null], [2, [0, null, null], null]]

Output

5```

### Solution :

```                        ```Solution in C++ :

int ans;
int go(Tree* root) {
if (!root) return 0;
int val = go(root->left) + go(root->right) + root->val;
ans = max(ans, val);
return val;
}
int solve(Tree* root) {
ans = 0;
go(root);
return ans;
}```
```

```                        ```Solution in Java :

import java.util.*;

class Solution {
public int solve(Tree root) {
dfs(root);
return max;
}
int max = 0;
public int dfs(Tree root) {
if (root == null)
return 0;

int left = dfs(root.left);
int right = dfs(root.right);

max = Math.max(max, root.val + left + right);
return root.val + left + right;
}
}```
```

```                        ```Solution in Python :

class Solution:
def solve(self, root):
sol = 0

def subsum(node):
nonlocal sol
lhs = subsum(node.left) if node.left else 0
rhs = subsum(node.right) if node.right else 0
res = node.val + lhs + rhs
sol = max(sol, res)
return res

subsum(root)
return sol```
```

## Find Merge Point of Two Lists

This challenge is part of a tutorial track by MyCodeSchool Given pointers to the head nodes of 2 linked lists that merge together at some point, find the node where the two lists merge. The merge point is where both lists point to the same node, i.e. they reference the same memory location. It is guaranteed that the two head nodes will be different, and neither will be NULL. If the lists share

## Inserting a Node Into a Sorted Doubly Linked List

Given a reference to the head of a doubly-linked list and an integer ,data , create a new DoublyLinkedListNode object having data value data and insert it at the proper location to maintain the sort. Example head refers to the list 1 <-> 2 <-> 4 - > NULL. data = 3 Return a reference to the new list: 1 <-> 2 <-> 4 - > NULL , Function Description Complete the sortedInsert function

## Reverse a doubly linked list

This challenge is part of a tutorial track by MyCodeSchool Given the pointer to the head node of a doubly linked list, reverse the order of the nodes in place. That is, change the next and prev pointers of the nodes so that the direction of the list is reversed. Return a reference to the head node of the reversed list. Note: The head node might be NULL to indicate that the list is empty.

## Tree: Preorder Traversal

Complete the preorder function in the editor below, which has 1 parameter: a pointer to the root of a binary tree. It must print the values in the tree's preorder traversal as a single line of space-separated values. Input Format Our test code passes the root node of a binary tree to the preOrder function. Constraints 1 <= Nodes in the tree <= 500 Output Format Print the tree's

## Tree: Postorder Traversal

Complete the postorder function in the editor below. It received 1 parameter: a pointer to the root of a binary tree. It must print the values in the tree's postorder traversal as a single line of space-separated values. Input Format Our test code passes the root node of a binary tree to the postorder function. Constraints 1 <= Nodes in the tree <= 500 Output Format Print the

## Tree: Inorder Traversal

In this challenge, you are required to implement inorder traversal of a tree. Complete the inorder function in your editor below, which has 1 parameter: a pointer to the root of a binary tree. It must print the values in the tree's inorder traversal as a single line of space-separated values. Input Format Our hidden tester code passes the root node of a binary tree to your \$inOrder* func