平衡二叉树

public class Solution {
    public boolean IsBalanced_Solution(TreeNode root) {
        return getDepth(root) != -1;
    }
    //用-1表示非平衡二叉树，只要发现，就停止迭代。
    private int getDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = getDepth(root.left);
        if (left == -1) {
            return -1;
        }
        int right = getDepth(root.right);
        if (right == -1) {
            return -1;
        }
        return Math.abs(left - right) > 1 ? -1 : 1 + Math.max(left, right);
    }
}