1609.奇偶树.md

方法一：BFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isEvenOddTree(TreeNode root) {
        Deque<TreeNode> queue = new LinkedList<>();
        int level = 0;
        if (root == null) return true;
        queue.addLast(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            int pre = level % 2 == 0 ? Integer.MIN_VALUE : Integer.MAX_VALUE;
            while (size != 0) {
                TreeNode node = queue.pollFirst();
                if (level % 2 == 0 && (node.val % 2 == 0 || node.val <= pre)) return false;
                if (level % 2 != 0 && (node.val % 2 != 0 || node.val >= pre)) return false;
                pre = node.val;
                if (node.left != null) queue.addLast(node.left);
                if (node.right != null) queue.addLast(node.right);
                size--;
            }
            level++;
        }
        return true;
    }
}

方法二：DFS

class Solution {
    Map<Integer, Integer> map = new HashMap<>();
    public boolean isEvenOddTree(TreeNode root) {
        return dfs(root, 0);
    }
    boolean dfs(TreeNode root, int idx) {
        boolean flag = idx % 2 == 0;
        int prev = map.getOrDefault(idx, flag ? 0 : 0x3f3f3f3f), cur = root.val;
        if (flag && (cur % 2 == 0 || cur <= prev)) return false;
        if (!flag && (cur % 2 != 0 || cur >= prev)) return false;
        map.put(idx, root.val);
        if (root.left != null && !dfs(root.left, idx + 1)) return false;
        if (root.right != null && !dfs(root.right, idx + 1)) return false;
        return true;
    }
}