[刷题]Balanced Binary Tree

[LintCode]Balanced Binary Tree

/** * 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) {        // 2015-3-23        return helper(root) != -1;    }    private int helper(TreeNode root) {    if (root == null) {    return 0;    }    // divide    int left = helper(root.left);    int right = helper(root.right);    // conquer    if (left == -1 || right == -1) {    return -1;    }    if  (Math.abs(left - right) > 1) {    return -1;    }    return Math.max(left, right) + 1;    }}