Given a binary tree, determine if it is height-balanced.

For this PRoblem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees ofeverynode never differ by more than 1.

這道題個人覺得不難，搞清楚平衡BTS的定義就好啦。

還有就是boolean method最后不要想當然的想著反正寫了>1就是false就想當然的return true，還是需要用method檢查的哦。

public class Solution {           public boolean isBalanced(TreeNode root) {          if(root == null){              return true;          }          // situation that unbalanced         if(Math.abs(getHeight(root.left)-getHeight(root.right)) > 1){              return false;          }          // recur test balance         return isBalanced(root.left) && isBalanced(root.right);    }        // getHeight method     private int getHeight(TreeNode root){          if(root == null){             return 0;         }          //aviod 0 we can promise root wont be null but root.left and root.right could be null here       return  1+Math.max(getHeight(root.left), getHeight(root.right));      }  }