鏈表的筆試題

單向鏈表節點定義：

typedef struct node
{
    int data;
    struct node *next;
}Node,*pNode;

雙向鏈表節點定義：

typedef struct node
{
    int data;
    struct node *next;
    struct node *pre;
}Node,*pNode;

鏈表逆序

非遞歸方法：

pNode RevertList(pNode head)
{
    if ((head == NULL) || (head->next == NULL))
        return head;
    pNode p1 = head;
    pNode p2 = p1->next;
    pNode p3 = p2->next;
    p1->next = NULL;
    while(p3 != NULL)
    {
        p2->next = p1;
        p1 = p2;
        p2 = p3;
        p3 = p3->next;
    }
    p2->next = p1;
    head = p2;
    return head;
}

遞歸方法：

pNode RevertList(pNode head)
{
    pNode p1 = NULL;
    if ( (head == NULL) || (head->next == NULL))
        return head;

    p1 = RevertList(head->next);
    head->next->next = head;
    head->next = NULL;
    return p1;
}

將2個有序的鏈表合併成一個有序鏈表

非遞歸方法：

pNode MergeList(pNode head1, pNode head2)
{
    if (head1 == NULL)
        return head2;
    if (head2 == NULL)
        return head1;

    pNode p1 = NULL;
    pNode p2 = NULL;
    pNode head = NULL;
    if (head1->data < head2->data)
    {
        head = head1;
        p1 = head1->next;
        p2 = head2;
    }
    else
    {
        head = head2;
        p1 = head1;
        p2 = head2->next;
    }
    pNode curNode = head;
    while((p1 != NULL) && (p2 != NULL))
    {
        if (p1->data < p2->data)
        {
            curNode->next = p1;
            curNode = p1;
            p1 = p1->next;
        }
        else
        {
            curNode->next = p2;
            curNode = p2;
            p2 = p2->next;
        }
    }
    if (p1 == NULL)
        curNode->next = p2;
    else
        curNode->next = p1;

    return head;
}

遞歸方法：

pNode MergeList(pNode head1, pNode head2)
{
    if (head1 == NULL)
        return head2;
    if (head2 == NULL)
        return head1;

    pNode head = NULL;
    if (head1->data < head2->data)
    {
        head = head1;
        head->next = MergeList(head1->next, head2);
    }
    else
    {
        head = head2;
        head->next = MergeList(head1, head2->next);
    }
    return head;
}

判斷一個單鏈表是有環的

bool CheckLoop(const pNode head)
{
    if (head == NULL)
        return false;
    pNode low = head;
    pNode fast = head->next;

    while((fast != NULL) && (fast->next != NULL))
    {
        if (low == fast)
            return true;
        low = low->next;
        fast = fast->next->next;
    }
    return false;
}