Populating Next Right Pointers in Each Node

因为是完全二叉树，所以根节点的左节点的next是根节点的右节点，右节点的next是根节点的左节点。递归实现。

    void connect(TreeLinkNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root != NULL){
            if(root->left)
                root->left->next = root->right;
            if(root->right)
                root->right->next = root->next ? root->next->left : NULL;
            connect(root->left);
            connect(root->right);
        }
    }