110.java

/**
 * 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 checkHeight(root)!=-1;
    }
    public static int checkHeight(TreeNode root) {
       if(root==null) return 0;
       int lHeight=checkHeight(root.left);
        if(lHeight==-1) return -1;
       int rHeight=checkHeight(root.right);
       if(rHeight==-1) return -1;
        if(Math.abs(lHeight-rHeight)>1) return -1;
        return Math.max(lHeight,rHeight)+1;
    }
}