Complete Binary Tree Inserter
<p>A <strong>complete binary tree</strong> is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.</p>

<p>Design an algorithm to insert a new node to a complete binary tree keeping it complete after the insertion.</p>

<p>Implement the <code>CBTInserter</code> class:</p>

<ul>
	<li><code>CBTInserter(TreeNode root)</code> Initializes the data structure with the <code>root</code> of the complete binary tree.</li>
	<li><code>int insert(int v)</code> Inserts a <code>TreeNode</code> into the tree with value <code>Node.val == val</code> so that the tree remains complete, and returns the value of the parent of the inserted <code>TreeNode</code>.</li>
	<li><code>TreeNode get_root()</code> Returns the root node of the tree.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0900-0999/0919.Complete%20Binary%20Tree%20Inserter/images/lc-treeinsert.jpg" style="width: 500px; height: 143px;" />
<pre>
<strong>Input</strong>
[&quot;CBTInserter&quot;, &quot;insert&quot;, &quot;insert&quot;, &quot;get_root&quot;]
[[[1, 2]], [3], [4], []]
<strong>Output</strong>
[null, 1, 2, [1, 2, 3, 4]]

<strong>Explanation</strong>
CBTInserter cBTInserter = new CBTInserter([1, 2]);
cBTInserter.insert(3); // return 1
cBTInserter.insert(4); // return 2
cBTInserter.get_root(); // return [1, 2, 3, 4]

</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree will be in the range <code>[1, 1000]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 5000</code></li>
	<li><code>root</code> is a complete binary tree.</li>
	<li><code>0 &lt;= val &lt;= 5000</code></li>
	<li>At most <code>10<sup>4</sup></code> calls will be made to <code>insert</code> and <code>get_root</code>.</li>
</ul>
Tree; Breadth-First Search; Design; Binary Tree
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
type CBTInserter struct {
	tree []*TreeNode
}

func Constructor(root *TreeNode) CBTInserter {
	q := []*TreeNode{root}
	tree := []*TreeNode{}
	for len(q) > 0 {
		for i := len(q); i > 0; i-- {
			node := q[0]
			q = q[1:]
			tree = append(tree, node)
			if node.Left != nil {
				q = append(q, node.Left)
			}
			if node.Right != nil {
				q = append(q, node.Right)
			}
		}
	}
	return CBTInserter{tree}
}

func (this *CBTInserter) Insert(val int) int {
	p := this.tree[(len(this.tree)-1)/2]
	node := &TreeNode{val, nil, nil}
	this.tree = append(this.tree, node)
	if p.Left == nil {
		p.Left = node
	} else {
		p.Right = node
	}
	return p.Val
}

func (this *CBTInserter) Get_root() *TreeNode {
	return this.tree[0]
}

/**
 * Your CBTInserter object will be instantiated and called as such:
 * obj := Constructor(root);
 * param_1 := obj.Insert(val);
 * param_2 := obj.Get_root();
 */