单链表操作

单链表操作

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链表节点定义：

struct node {
	int value;
	struct node* next;
};

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#### 反转单链表

struct node* reverse(struct node* list)
{
    if (NULL == list) {
        return NULL;
    }

    struct node* list_r = list;
    list = list->next;
    list_r->next = NULL;

    struct node* p;
    while (NULL != list) {
        p = list;
        list = list->next;
        p->next = list_r;
        list_r = p;	
    }

    return list_r;
}

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#### 合并单链表

struct node* merge(struct node* list1, struct node* list2)
{
    if (NULL == list1 && NULL == list2) {
        return NULL;
    }

    if (NULL == list1) {
        return list2;
    }
    
    if (NULL == list2) {
        return list1;
    }

    struct node* list;
    struct node* p;
    if (list1->value <= list2->value) {
        list = list1;
        list1 = list1->next;
    } else {
        list = list2;
        list2 = list2->next;
    }
    
    p = list;
    
    while (NULL != list1 && NULL != list2) {
        if (list1->value <= list2->value) {
            p->next = list1;
            p = list1;
            list1 = list1->next;
        } else {
            p->next = list2;
            p = list2;
            list2 = list2->next;
        }	
    }
    
    if (NULL != list1) {
        p->next = list1;
    }

    if (NULL != list2) {
        p->next = list2;
    }

    return list;	
}

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#### 判断单链表是否存在环

bool has_loop(struct node* list)
{
    if (NULL == list) {
        return false;
    }

    struct node* p1 = list;
    struct node* p2 = list;

    while (NULL != p2->next) {
        p2 = p2->next;
        if (NULL != p2->next) {
            p2 = p2->next;
        } else {
            return false;
        }
        
        p1 = p1->next;

        if (p2 == p1) {
            return true;
        }
    }
    return false;
}

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#### 查找有环单链表的环开始点

struct node* find_loop_port(struct node* list)
{
    if (NULL == list) {
        return NULL;
    }

    struct node* p1 = list;
    struct node* p2 = list;

    bool hasloop = false;
    while (NULL != p2->next) {
        p2 = p2->next;
        if (NULL != p2->next) {
            p2 = p2->next;
        } else {
            break;
        }
        
        p1 = p1->next;

        if (p2 == p1) {
            hasloop = true;
            break;
        }
    }
    
    struct node* p3 = NULL;
    if (true == hasloop) {
        if (p2 == list) {
            return list;
        } else {
            p3 = list;
            while (true) {
                p2 = p2->next;
                p3 = p3->next;

                if (p2 == p3) {
                    break;
                }
            }
        }
    }
    return p3;
}

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#### 移除单链表的特定节点

struct node* remove_if(struct node* list, bool(*cond_func)(struct node*))
{
    if (NULL == list) {
        return list;
    }

    struct node** ppNode = &list;
    for (struct node* pNode = *ppNode; NULL != pNode; pNode = *ppNode) {
        if (true == cond_func(pNode)) {
            if (pNode == list) {
                list = pNode->next;
            }
            *ppNode = pNode->next;
            free(pNode);
        } else {
            ppNode = &(pNode->next);
        }
    }

    return list;
}

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