LeetCode in Kotlin

1609. Even Odd Tree

Medium

A binary tree is named Even-Odd if it meets the following conditions:

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

Given the root of a binary tree, return true if the binary tree is Even-Odd, otherwise return false.

Example 1:

Input: root = [1,10,4,3,null,7,9,12,8,6,null,null,2]

Output: true

Explanation: 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.

Example 2:

Input: root = [5,4,2,3,3,7]

Output: false

Explanation: 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.

Example 3:

Input: root = [5,9,1,3,5,7]

Output: false

Explanation: Node values in the level 1 should be even integers.

Constraints:

• The number of nodes in the tree is in the range [1, 105].
• 1 <= Node.val <= 106

Solution

import com_github_leetcode.TreeNode

/*
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    private val comp: MutableList<Int> = ArrayList()

    fun isEvenOddTree(root: TreeNode?): Boolean {
        return find(root, 0)
    }

    private fun find(root: TreeNode?, height: Int): Boolean {
        if (root == null) {
            return true
        }
        if (height % 2 == 0 && root.`val` % 2 == 0 || height % 2 == 1 && root.`val` % 2 == 1) {
            return false
        }
        if (comp.size == height) {
            comp.add(root.`val`)
        } else {
            if (height % 2 == 0) {
                if (comp[height] >= root.`val`) {
                    return false
                } else {
                    comp[height] = root.`val`
                }
            } else {
                if (comp[height] <= root.`val`) {
                    return false
                } else {
                    comp[height] = root.`val`
                }
            }
        }
        return find(root.left, height + 1) && find(root.right, height + 1)
    }
}

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