1516. Move Sub-Tree of N-Ary Tree

https://leetcode.com/problems/move-sub-tree-of-n-ary-tree

Description

Given the root of an N-ary tree of unique values, and two nodes of the tree p and q.

You should move the subtree of the node p to become a direct child of node q. If p is already a direct child of q, don't change anything. Node p must be the last child in the children list of node q.

Return the root of the tree after adjusting it.

There are 3 cases for nodes p and q:

1. Node q is in the sub-tree of node p.

2. Node p is in the sub-tree of node q.

3. Neither node p is in the sub-tree of node q nor node q is in the sub-tree of node p.

In cases 2 and 3, you just need to move p (with its sub-tree) to be a child of q, but in case 1 the tree may be disconnected, thus you need to reconnect the tree again. Please read the examples carefully before solving this problem.

Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).

For example, the above tree is serialized as [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14].

Example 1:

**Input:** root = [1,null,2,3,null,4,5,null,6,null,7,8], p = 4, q = 1
**Output:** [1,null,2,3,4,null,5,null,6,null,7,8]
**Explanation:** This example follows the second case as node p is in the sub-tree of node q. We move node p with its sub-tree to be a direct child of node q.
Notice that node 4 is the last child of node 1.

Example 2:

**Input:** root = [1,null,2,3,null,4,5,null,6,null,7,8], p = 7, q = 4
**Output:** [1,null,2,3,null,4,5,null,6,null,7,8]
**Explanation:** Node 7 is already a direct child of node 4. We don't change anything.

Example 3:

**Input:** root = [1,null,2,3,null,4,5,null,6,null,7,8], p = 3, q = 8
**Output:** [1,null,2,null,4,5,null,7,8,null,null,null,3,null,6]
**Explanation:** This example follows case 3 because node p is not in the sub-tree of node q and vice-versa. We can move node 3 with its sub-tree and make it as node 8's child.

Example 4:

**Input:** root = [1,null,2,3,null,4,5,null,6,null,7,8], p = 2, q = 7
**Output:** [1,null,7,3,null,2,null,6,null,4,5,null,null,8]
**Explanation:** Node q is in the sub-tree of node p, so this is case 1.
The first step, we move node p (with all of its sub-tree except for node q) and add it as a child to node q.
Then we will see that the tree is disconnected, you need to reconnect node q to replace node p as shown.

Example 5:

**Input:** root = [1,null,2,3,null,4,5,null,6,null,7,8], p = 1, q = 2
**Output:** [2,null,4,5,1,null,7,8,null,null,3,null,null,null,6]
**Explanation:** Node q is in the sub-tree of node p, so this is case 1.
The first step, we move node p (with all of its sub-tree except for node q) and add it as a child to node q.
As node p was the root of the tree, node q replaces it and becomes the root of the tree.

Constraints:

• The total number of nodes is between [2, 1000].

• Each node has a unique value.

• p != null

• q != null

• p and q are two different nodes (i.e. p != q).

ac