public class Solution {
    public boolean isBalanced(TreeNode root) {
        return getDepth(root)!=-1;
    }
    
    public int getDepth(TreeNode root){
        if(root==null){
            return 0;
        }
        int left = getDepth(root.left);
        if(left!=-1){
            int right = getDepth(root.right);
            if(right!=-1){
                return Math.abs(left-right)<=1?1+Math.max(left,right):-1;
            }
        }
        return -1;
    }
}