【算法题hot】对称二叉树

给你一个二叉树的根节点 root ， 检查它是否轴对称。

输入：root = [1,2,2,3,4,4,3]
输出：true

public class LC018_101_isSymmetric_01 {

    //递归实现
    public static boolean isSymmetric(TreeNode root) {
        if (root == null || (root.left == null && root.right == null)) {
            return true;
        }
        return dfs(root.left, root.right);
    }

    private static boolean dfs(TreeNode left, TreeNode right) {
        if (left == null && right == null) {
            return true;
        }
        if (left == null || right == null) {
            return false;
        }
        if (left.val != right.val) {
            return false;
        }
        return dfs(left.left, right.right) && dfs(left.right, right.left);
    }


    public static void main(String[] args) {
        TreeNode node = TreeNode.generateRandomBST(1, 1000, 3);
        TreeNode.printTree(node);
        System.out.println(isSymmetric(node));
        //TreeNode.printTree(node);
    }
}

public class LC018_101_isSymmetric_02 {
    //队列实现
    public static boolean isSymmetric(TreeNode root) {
        if (root == null || (root.left == null && root.right == null)) {
            return true;
        }
        LinkedList queue = new LinkedList<>();
        queue.add(root.left);
        queue.add(root.right);

        while (!queue.isEmpty()) {
            TreeNode left = queue.removeFirst();
            TreeNode right = queue.removeFirst();
            if (left == null && right == null) {
                continue;
            }
            if (left == null || right == null) {
                return false;
            }
            if (left.val != right.val) {
                return false;
            }
            queue.add(left.left);
            queue.add(right.right);
            queue.add(left.right);
            queue.add(right.left);
        }
        return true;
    }

    public static void main(String[] args) {
        TreeNode node = TreeNode.generateRandomBST(1, 1000, 3);
        TreeNode.printTree(node);
        System.out.println(isSymmetric(node));
        //TreeNode.printTree(node);
    }
}