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 of every node never differ by more than 1.
这道题个人觉得不难，搞清楚平衡BTS的定义就好啦。
还有就是boolean method最后不要想当然的想着反正写了>1就是false就想当然的return true，还是需要用method检查的哦。
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));
}
}