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.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 */
var CBTInserter = function (root) {
    this.tree = [];
    if (root === null) {
        return;
    }
    const q = [root];
    while (q.length) {
        const t = [];
        for (const node of q) {
            this.tree.push(node);
            node.left !== null && t.push(node.left);
            node.right !== null && t.push(node.right);
        }
        q.splice(0, q.length, ...t);
    }
};

/**
 * @param {number} val
 * @return {number}
 */
CBTInserter.prototype.insert = function (val) {
    const p = this.tree[(this.tree.length - 1) >> 1];
    const node = new TreeNode(val);
    this.tree.push(node);
    if (p.left === null) {
        p.left = node;
    } else {
        p.right = node;
    }
    return p.val;
};

/**
 * @return {TreeNode}
 */
CBTInserter.prototype.get_root = function () {
    return this.tree[0];
};

/**
 * Your CBTInserter object will be instantiated and called as such:
 * var obj = new CBTInserter(root)
 * var param_1 = obj.insert(val)
 * var param_2 = obj.get_root()
 */
