110. 平衡二叉樹

class Solution {
public:
    bool isBalanced(TreeNode* root) 
    {
        return p(root)!=-1;
    }
    int p(TreeNode* root){
        if(root==NULL)return 0;
        int l=p(root->left);
        if(l==-1)return -1;
        int r=p(root->right);
        if(r==-1)return -1;
        return abs(l-r)>1?-1:1+max(l,r);
    }
};