非递归算法：

    2. {
    3.     if (NULL == head)
    4.     {
    5.         return;
    7.     list_node *curr = head;
    8.     list_node *next = head->next;
    9.     list_node *prev = NULL;
    10.     while (next != NULL) {
    11.         curr->next = prev;
    12.         curr = next;
    13.         next = curr->next;
    14.     }
    16.     curr->next = prev;