110. Balanced Binary Tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int re = 0;
    public boolean isBalanced(TreeNode root) {
        if(root == null) return true;
        return res(root)!=-1;
    }
    
    public int res(TreeNode node){
        if(node == null) return 0;
            
        int left = res(node.left);
        if(left == -1) return -1;
        int right = res(node.right);
        if(right == -1) return -1;
        if(Math.abs(left-right)>=2) return -1;
        return Math.max(left, right) + 1; 
    }
    

}

   

//bottom up
/*
public type Traverse() {

   node.left =      // left = 
   node.right =     // right =
   return node      // return left - right
}

*/