4. Balanced Binary Tree

Given a binary tree, determine if it is A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one..

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: true

Example 2:

Input: root = [1,2,2,3,3,null,null,4,4]
Output: false

Example 3:

Input: root = []
Output: true

Constraints:

• The number of nodes in the tree is in the range [0, 5000].
• -104 <= Node.val <= 104

Approach

• We will return -1 if it is not balanced and rest is simple dfs recursion

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