LeetCode 判断一个数是否为平衡二叉树 Balanced Binary Tree

package Level1;
import Utility.TreeNode;

/**
* Balanced Binary Tree 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.
*
*/
public class S110 {

public static void main(String[] args) {

}

public boolean isBalanced(TreeNode root) {
if(root == null){
return true;
}
// 如果子树高度差大于1，则不平衡
if(Math.abs(depth(root.left)-depth(root.right)) > 1){
return false;
}
// 递归检查左子树和右子树的平衡性
return isBalanced(root.left) && isBalanced(root.right);
}

// 帮助方法，返回树的高度
private int depth(TreeNode root){
if(root == null){
return 0;
}
return 1 + Math.max(depth(root.left), depth(root.right));
}
}

/**
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean isBalanced(TreeNode root) {
if(root == null){
return true;
}
if(root.left==null && root.right==null){
return true;
}
if(Math.abs(depth(root.left)-depth(root.right)) > 1){
return false;
}
return isBalanced(root.left) && isBalanced(root.right);
}

public int depth(TreeNode root){
if(root==null){
return 0;
}
return 1+Math.max(depth(root.left), depth(root.right));
}
}