Balanced Binary Tree

Problem

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

Given binary tree A={3,9,20,#,#,15,7}, B={3,#,20,15,7}

A)  3            B)    3
    / \                  \
  9  20                 20
    /  \                / \
    15   7              15  7

The binary tree A is a height-balanced binary tree, but B is not.

Code - Java

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *   public int val;
 *   public TreeNode left, right;
 *   public TreeNode(int val) {
 *     this.val = val;
 *     this.left = this.right = null;
 *   }
 * }
 */
public class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: True if this Binary tree is Balanced, or false.
     */
    public boolean isBalanced(TreeNode root) {
        return balanced(root) != -1;
    }

    private int balanced(TreeNode root) {
        if (root == null) {
            return 0;
        }

        int left = balanced(root.left);
        int right = balanced(root.right);

        if (left == -1 || right == -1) {
            return -1;
        }

        if (Math.abs(left - right) <= 1) {
            return Math.max(left, right) + 1;
        } else {
            return -1;
        }
    }
}

Online Judge

LintCode: https://www.lintcode.com/en/problem/balanced-binary-tree/