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1609. Even Odd Tree.md

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1609. Even Odd Tree

the second one in Weekly Contest 209.

Difficulty : Medium

Related Topics : Tree

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:

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:

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 the level 2 must be in strictly increasing order, so the tree is not Even-Odd.

Example 3:

3

Input: root = [5,9,1,3,5,7]
Output: false
Explanation: Node values in the level 1 should be even integers.

Example 4:

Input: root = [1]
Output: true

Example 5:

Input: root = [11,8,6,1,3,9,11,30,20,18,16,12,10,4,2,17]
Output: true

Constraints:

  • The number of nodes in the tree is in the range [1, 10^5].
  • 1 <= Node.val <= 10^6

Solution

  • mine
    • Java
      • Runtime: 7 ms, faster than 99.92%, Memory Usage: 56.3 MB, less than 5.00% of Java online submissions 
        // O(N)time
// O(maxsize(level))space
public boolean isEvenOddTree(TreeNode root) {
    LinkedList<TreeNode> list = new LinkedList<>();
    list.add(root);
    int level = 0;
    while(!list.isEmpty()){
        int size = list.size();
        boolean large = level % 2 == 0;
        int f = large ? Integer.MIN_VALUE : Integer.MAX_VALUE;
        while(size > 0){
            TreeNode node = list.removeFirst();
            if(node.left != null) list.add(node.left);
            if(node.right != null) list.add(node.right);
            if(large){
                if(node.val % 2 == 0) return false;
                if(node.val > f) f = node.val;
                else return false;
            }else{
                if(node.val % 2 != 0) return false;
                if(node.val < f) f = node.val;
                else return false;
            }
            size--;
        }
        level++;
    }
    return true;
}