[LeetCode] 543. Diameter of Binary Tree

int dbHelp(TreeNode *r,int &res)
{
	if(!r)return 0;
	int lh=dbHelp(r->left,res)+1;
	int rh=dbHelp(r->right,res)+1;
	res=max(res,lh+rh-2);
	return max(lh,rh);
}
int diameterOfBinaryTree(TreeNode* root)
{
	int res=0;
	dbHelp(root,res);
	return res;
}