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.


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

Example 1


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



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;
    return ans;

                        Solution in Java :

import java.util.*;

class Solution {
    public int solve(Tree 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

        return sol

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