解题思路

class Solution {
   public boolean isBalanced(TreeNode root) {
        return depth(root)!=-1;
    }
    public int depth(TreeNode root){
        if(root==null) return 0;
        int left = depth(root.left);
        if(left==-1) return -1;
        int right = depth(root.right);
        if(right==-1) return -1;
        return Math.abs(left-right)<2?Math.max(left,right)+1:-1;
    }
}