**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
```

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