Lintcode93-Balanced Binary Tree-Easy

93. Balanced Binary Tree

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

Example  1:
	Input: tree = {1,2,3}
	Output: true

	Explanation:
	This is a balanced binary tree.
		  1
		 / \
		2  3

Example  2:
	Input: tree = {3,9,20,#,#,15,7}
	Output: true

	Explanation:
	This is a balanced binary tree.
		  3
		 / \
		9  20
		  /  \
		 15   7 

Example  3:
	Input: tree = {1,#,2,3,4}
	Output: false

	Explanation:
	This is not a balanced tree.
	The height of node 1's right sub-tree is 2 but left sub-tree is 0.
		  1
		   \
		   2
		  /  \
		 3   4

 

分治法：

/**
 * 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 maxDepth(root) != -1;
    }

    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int right = maxDepth(root.right);
        int left = maxDepth(root.left);
        if (right == -1 || left == -1 || Math.abs(right-left) > 1) {
            return -1;
        }
        return Math.max(right,left) + 1;
    }
}