求二叉树中节点的最大距离

struct Node{
Node *pLeft;
Node *pRight;
};

int maxLen = 0;

int treeDepth(Node *pRoot, &maxLen){
if(pRoot == NULL)
return -1;
int leftDepth = treeDepth(pRoot->pLeft, maxLen) + 1;
int rightDepth = treeDepth(pRoot->pRight, maxLen) + 1;
if(maxLen < leftDepth + rightDepth)
maxLen = leftDepth + rightDepth;
return leftDepth > rightDepth ? leftDepth : rightDepth;
}