Leetcode - 110 判断二叉树是否为平衡二叉树
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.
解决方案(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; } }
自创版本:
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)); } }