1609. Even Odd Tree

Description

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

 

Solutions

Solution: Breadth-First Search

• Time complexity: O(n)
• Space complexity: O(n)

 

JavaScript

/**
 * 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
 * @return {boolean}
 */
const isEvenOddTree = function (root) {
  const queue = [root];
  let currentLevel = 'even';

  while (queue.length) {
    const size = queue.length;
    const isEvenLevel = currentLevel === 'even';
    let preNodeVal = 0;

    for (let index = 0; index < size; index++) {
      const { val, left, right } = queue.shift();
      const isOddVal = val % 2;

      if (isEvenLevel) {
        if (!isOddVal) return false;
        if (preNodeVal && preNodeVal >= val) return false;
      } else {
        if (isOddVal) return false;
        if (preNodeVal && preNodeVal <= val) return false;
      }
      preNodeVal = val;
      left && queue.push(left);
      right && queue.push(right);
    }
    currentLevel = isEvenLevel ? 'odd' : 'even';
  }
  return true;
};