class Solution {
    public boolean isBalanced(TreeNode root) {
        if (root == null)  return true;
        // Height Function will return -1, when it’s an unbalanced tree...
		    if (Height(root) == -1)  return false;
		return true;
	}

	public int Height(TreeNode root) {
		if (root == null)  return 0;
       
		int leftHeight = Height(root.left);
		int rightHight = Height(root.right);
        // In case of left subtree or right subtree unbalanced, return -1...
		if (leftHeight == -1 || rightHight == -1)  return -1;
        // If their heights differ by more than ‘1’, return -1...
    if (Math.abs(leftHeight - rightHight) > 1)  return -1;
        // Otherwise, return the height of this subtree as max(leftHeight, rightHight) + 1...
		return Math.max(leftHeight, rightHight) + 1;
    }
}

public int height(TreeNode node) {
    // 如果節點為空，返回高度 0
    if (node == null) {
        return 0;
    }

    // 遞歸計算左子樹的高度
    int leftHeight = height(node.left);

    // 遞歸計算右子樹的高度
    int rightHeight = height(node.right);

    // 返回左子樹和右子樹中較大的高度加 1
    return Math.max(leftHeight, rightHeight) + 1;
}