// At DoorDash, menus are updated daily even hourly to keep them up-to-date. Each menu can be regarded as a tree. When the merchant sends us the latest menu, can we calculate how many nodes has changed?

// Assume each Node structure is as below:

// class Node {
// String key;
// int value;
// boolean active;
// List children;
// }
// Assume there are no duplicate nodes with the same key.

// Output: Return the number of changed nodes in the tree.

// Example 1
// Existing Menu in our system:

// Existing tree
// a(1, T)
// /
// b(2, T) c(3, T)
// / \
// d(4, T) e(5, T) f(6, T)
// ( Legend - a(1, T) a is the key, 1 is the value, T is True for active status )

// New Menu sent by the Merchant:

// New tree
// a(1, T)
//
// c(3, F)
//
// f(66, T)
// Expected Answer: 5 Explanation: Node b, Node d, Node e are automatically set to inactive. The active status of Node c and the value of Node f changed as well.

// Example 2
// Existing Menu in our system:

// Existing tree
// a(1, T)
// /
// b(2, T) c(3, T)
// / \
// d(4, T) e(5, T) g(7, T)
// New Menu sent by the Merchant:

// New tree
// a(1, T)
// /
// b(2, T) c(3, T)
// / | \
// d(4, T)e(5, T)f(6, T) g(7, F)
// Expected Answer: 2 Explanation: Node f is a newly-added node. Node g changed from Active to inactive

I was asked this question in my phone screen. Could not solve it completely. Any Suggestions?