LeetCode121|单值二叉树

输入：[1,1,1,1,1,null,1]
输出：true

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class IsUnivalTreeTest {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        TreeNode t2 = new TreeNode(1);
        TreeNode t3 = new TreeNode(1);
        TreeNode t4 = new TreeNode(1);
        TreeNode t5 = new TreeNode(1);
        TreeNode t6 = new TreeNode(1);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t5;
        t3.right = t6;
        boolean univalTree = isUnivalTree2(t1);
        System.out.println("univalTree = " + univalTree);


    }

    public static boolean isUnivalTree(TreeNode root) {
        if (root == null) {
            return true;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        List<Integer> list = new ArrayList<>();
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode treeNode = queue.poll();
                list.add(treeNode.val);
                if (treeNode.left != null) {
                    queue.add(treeNode.left);
                }
                if (treeNode.right != null) {
                    queue.add(treeNode.right);
                }
            }
        }
        Integer val = list.get(0);
        for (int num : list) {
            if (num != val) {
                return false;
            }
        }
        return true;
    }

    public static boolean isUnivalTree2(TreeNode root) {
        if (root == null) {
            return true;
        }
        if (root.left != null && root.val != root.left.val) {
            return false;
        }
        if (root.right != null && root.val != root.right.val) {
            return false;
        }
        return isUnivalTree(root.left) && isUnivalTree(root.right);
    }
}