110. 平衡二叉树

给定一个二叉树，判断它是否是高度平衡的二叉树。
本题中，一棵高度平衡二叉树定义为：

一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过 1 。

  1. /**
  2.  * Definition for a binary tree node.
  3.  * public class TreeNode {
  4.  *     int val;
  5.  *     TreeNode left;
  6.  *     TreeNode right;
  7.  *     TreeNode() {}
  8.  *     TreeNode(int val) { this.val = val; }
  9.  *     TreeNode(int val, TreeNode left, TreeNode right) {
  10.  *         this.val = val;
  11.  *         this.left = left;
  12.  *         this.right = right;
  13.  *     }
  14.  * }
  15.  */
  16. class Solution {
  17.     public boolean isBalanced(TreeNode root) {
  18.          if (root == null) {
  19.             return true;
  20.         } else {
  21.             return Math.abs(height(root.left) - height(root.right)) <= 1 && isBalanced(root.left) && isBalanced(root.right);
  22.         }
  23.     }
  25.     public int height(TreeNode root) {
  26.         if (root == null) {
  27.             return 0;
  28.         } else {
  29.             return Math.max(height(root.left), height(root.right)) + 1;
  30.         }
  31.     }
  33. // 作者：LeetCode-Solution
  34. // 链接：https://leetcode-cn.com/problems/balanced-binary-tree/solution/ping-heng-er-cha-shu-by-leetcode-solution/
  36.     }
  37. }
  1. /**
  2.  * Definition for a binary tree node.
  3.  * public class TreeNode {
  4.  *     int val;
  5.  *     TreeNode left;
  6.  *     TreeNode right;
  7.  *     TreeNode() {}
  8.  *     TreeNode(int val) { this.val = val; }
  9.  *     TreeNode(int val, TreeNode left, TreeNode right) {
  10.  *         this.val = val;
  11.  *         this.left = left;
  12.  *         this.right = right;
  13.  *     }
  14.  * }
  15.  */
  16. class Solution {
  17.     public boolean isBalanced(TreeNode root) {
  18.         return height(root) >= 0;
  19.     }
  21.     public int height(TreeNode root) {
  22.         if (root == null) {
  23.             return 0;
  24.         }
  25.         int leftHeight = height(root.left);
  26.         int rightHeight = height(root.right);
  27.         if (leftHeight == -1 || rightHeight == -1 || Math.abs(leftHeight - rightHeight) > 1) {
  28.             return -1;
  29.         } else {
  30.             return Math.max(leftHeight, rightHeight) + 1;
  31.         }
  32.     }
  34. // 作者：LeetCode-Solution
  35. // 链接：https://leetcode-cn.com/problems/balanced-binary-tree/solution/ping-heng-er-cha-shu-by-leetcode-solution/
  37. }