我在一本书中看到了这个问题（破解编码面试）。建议代码为：

public boolean isBalanced(Node root) {

    if(root == null)
        return true;

    int leftHeight = getHeight(root.left);
    System.out.println("left height: " + leftHeight);
    int rightHeight = getHeight(root.right);
    System.out.println("right height: " + rightHeight);
    int diff = Math.abs(leftHeight - rightHeight);

    // check if difference in height is more than 1
    if (diff > 1)
        return false;

    // check if left and right subtrees are balanced
    else 
        return isBalanced(root.left) && isBalanced(root.right);

我不明白的是为什么我们需要returnisbalanced（root.left）和&isbalanced（root.right）。仅仅检查高度就足够了吗？如果高度大于1，返回false，否则返回true？