Description
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]:
tree
Return true.
Example 2:
Given the following tree [1,2,2,3,3,null,null,4,4]:
tree
Return false.
Solution
DFS, time O(n), space O(h)
/**
* 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;
}
return isBalanced(root.left) && isBalanced(root.right)
&& Math.abs(depth(root.left) - depth(root.right)) <= 1;
}
private int depth(TreeNode root) {
if (root == null) {
return 0;
}
return 1 + Math.max(depth(root.left), depth(root.right));
}
}
