110. Balanced Binary Tree
Tags: ‘Tree’, ‘Depth-first Search’
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.
Solution
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
if (root == null) return true; // end case
if (root != null && Math.abs(maxDepth(root.left) - maxDepth(root.right)) > 1)
return false;
return isBalanced(root.left) && isBalanced(root.right);
}
private int maxDepth(TreeNode node) {
if (node == null) return 0;
return Math.max(maxDepth(node.left), maxDepth(node.right)) + 1;
}
}