Leetcode - 110 判斷二叉樹是否爲平衡二叉樹

110. 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.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

3
   / \
  9  20
    /  \
   15   7

Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

 

解決方案（完美版）：

 

class Solution { public boolean isBalanced(TreeNode root) { return helper(root) != -1; } public int helper(TreeNode root){ if(root == null) return 0; int left = helper(root.left); int right = helper(root.right); if(left == -1 || right == -1 || Math.abs(left - right) > 1) return -1; return Math.max(left, right) + 1; } }

 

自創版本：

class Solution { public boolean isBalanced(TreeNode root) { if(root == null){ return true; } return (Math.abs(maxNodeLength(root.left) - maxNodeLength(root.right)) <= 1) && isBalanced(root.left) && isBalanced(root.right); } public int maxNodeLength(TreeNode root){ if(root == null){ return 0; } return 1 + Math.max(maxNodeLength(root.left),maxNodeLength(root.right)); } }