# Enlarge BST - Amazon Top Interview Questions

### Problem Statement :

```Given a binary search tree root, replace every node's value v by its value plus the sum of all other values in the tree that are greater than v.

Constraints

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

Example 1

Input

root = [4, [2, [1, null, null], [3, null, null]], [5, null, null]]

Output

[9, [14, [15, null, null], [12, null, null]], [5, null, null]]```

### Solution :

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

int acc;

void post_order(Tree* u) {
if (!u) return;
post_order(u->right);
acc += u->val;
u->val = acc;
post_order(u->left);
}

Tree* solve(Tree* root) {
acc = 0;
post_order(root);
return root;
}```
```

```                        ```Solution in Java :

import java.util.*;

/**
* public class Tree {
*   int val;
*   Tree left;
*   Tree right;
* }
*/
class Solution {
private int sum = 0;
public Tree solve(Tree root) {
dfs(root);
return root;
}

private void dfs(Tree node) {
if (node == null)
return;
dfs(node.right);
int val = node.val;
node.val += sum;
sum += val;
dfs(node.left);
}
}```
```

```                        ```Solution in Python :

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

def dfs(root):
nonlocal ans
if not root:
return None
dfs(root.right)
ans += root.val
root.val = ans
dfs(root.left)

dfs(root)
return root```
```

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