# 你所不知道的 C 語言: linked list 和非連續記憶體 - 筆記
Jserv的教材[https://hackmd.io/@sysprog/c-linked-list](https://)

void remove_list_node(List *list, Node *target)
{
    Node *prev = NULL;
    Node *current = list->head;
    // Walk the list
    while (current != target) {
        prev = current;
        current = current->next;
    }
    // Remove the target by updating the head or the previous node.
    if (!prev)
        list->head = target->next;
    else
        prev->next = target->next;
}

其中的==if (!prev)==是針對如果是第一筆資料的情況，==else==則是指==中間的資料==
* 有品味的版本，指標的指標 (或稱「間接指標」，即 indirect pointer)

void remove_list_node(List *list, Node *target)
{
    // The "indirect" pointer points to the *address*
    // of the thing we'll update.
    Node **indirect = &list->head;
    // Walk the list, looking for the thing that 
    // points to the node we want to remove.
    while (*indirect != target)
        indirect = &(*indirect)->next;
    *indirect = target->next;
}

indirect = &(*indirect)->next;

其中這裡是先取得(*indirect)的==next==接著再去取位址
可參考這裡[https://hackmd.io/@sysprog/c-pointer](https://)，幫助理解原理

以下部分不太理解

static inline Node *move(Node *cur) { return cur ? cur->next : NULL; }

bool cycle_finding(Node *HEAD, Node **TAIL, int *length, int *mu, int *lambda) {
    // lambda is length
    // mu is the meet node's index
    Node *tortoise = move(HEAD);
    Node *hare = move(move(HEAD));

    // get meet point
    while (hare && tortoise) {    /* Maybe while (hare && tortoise && (hare != tortoise)) ?*/
        tortoise = move(tortoise);
        hare = move(move(hare));
    }

    // not loop
    if (!hare) {
        *TAIL = NULL;
        *length = 0;
        tortoise = HEAD;
        while (tortoise && (tortoise = move(tortoise)))
            (*length)++;
        return false;
    }

    // get mu
    *mu = 0;
    tortoise = HEAD;
    while (tortoise != hare) {
        (*mu)++;
        tortoise = tortoise->next;
        hare = hare->next;
    }

    // get lambda
    *lambda = 1;
    tortoise = move(tortoise);
    *TAIL = tortoise;
    while (tortoise != hare) {
        *TAIL = tortoise;
        (*lambda)++;
        tortoise = move(tortoise);
    }
    *length = *mu + *lambda;

    return true;
}