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 left and right subtrees of every node differ in height by no more than 1.
Examples
Input: root = [3,9,20,null,null,15,7] Output: true
Input: root = [1,2,2,3,3,null,null,4,4] Output: false
Input: root = [] Output: true
Constraints
The number of nodes in the tree is in the range [0, 5000]. -104 <= Node.val <= 104
Java Solution
Bottom Up Recursion
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
return height(root) != -1;
}
public int height(TreeNode root) {
if(root == null) return 0;
int left = height(root.left);
int right = height(root.right);
if (Math.abs(left - right) > 1 || left == -1 || right == -1) return -1;
return Math.max(left, right) + 1;
}
}