Even Odd Tree
<p>A binary tree is named <strong>Even-Odd</strong> if it meets the following conditions:</p>

<ul>
	<li>The root of the binary tree is at level index <code>0</code>, its children are at level index <code>1</code>, their children are at level index <code>2</code>, etc.</li>
	<li>For every <strong>even-indexed</strong> level, all nodes at the level have <strong>odd</strong> integer values in <strong>strictly increasing</strong> order (from left to right).</li>
	<li>For every <b>odd-indexed</b> level, all nodes at the level have <b>even</b> integer values in <strong>strictly decreasing</strong> order (from left to right).</li>
</ul>

<p>Given the <code>root</code> of a binary tree, <em>return </em><code>true</code><em> if the binary tree is <strong>Even-Odd</strong>, otherwise return </em><code>false</code><em>.</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1600-1699/1609.Even%20Odd%20Tree/images/sample_1_1966.png" style="width: 362px; height: 229px;" />
<pre>
<strong>Input:</strong> root = [1,10,4,3,null,7,9,12,8,6,null,null,2]
<strong>Output:</strong> true
<strong>Explanation:</strong> The node values on each level are:
Level 0: [1]
Level 1: [10,4]
Level 2: [3,7,9]
Level 3: [12,8,6,2]
Since levels 0 and 2 are all odd and increasing and levels 1 and 3 are all even and decreasing, the tree is Even-Odd.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1600-1699/1609.Even%20Odd%20Tree/images/sample_2_1966.png" style="width: 363px; height: 167px;" />
<pre>
<strong>Input:</strong> root = [5,4,2,3,3,7]
<strong>Output:</strong> false
<strong>Explanation:</strong> The node values on each level are:
Level 0: [5]
Level 1: [4,2]
Level 2: [3,3,7]
Node values in level 2 must be in strictly increasing order, so the tree is not Even-Odd.
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1600-1699/1609.Even%20Odd%20Tree/images/sample_1_333_1966.png" style="width: 363px; height: 167px;" />
<pre>
<strong>Input:</strong> root = [5,9,1,3,5,7]
<strong>Output:</strong> false
<strong>Explanation:</strong> Node values in the level 1 should be even integers.
</pre>

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

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 10<sup>5</sup>]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 10<sup>6</sup></code></li>
</ul>
Tree; Breadth-First Search; Binary Tree
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isEvenOddTree(root *TreeNode) bool {
	even := true
	q := []*TreeNode{root}
	for len(q) > 0 {
		var prev int = 1e7
		if even {
			prev = 0
		}
		for n := len(q); n > 0; n-- {
			root = q[0]
			q = q[1:]
			if even && (root.Val%2 == 0 || prev >= root.Val) {
				return false
			}
			if !even && (root.Val%2 == 1 || prev <= root.Val) {
				return false
			}
			prev = root.Val
			if root.Left != nil {
				q = append(q, root.Left)
			}
			if root.Right != nil {
				q = append(q, root.Right)
			}
		}
		even = !even
	}
	return true
}