【力扣 简单 C】141. 环形链表

目录

题目

解法一：记录遍历过的结点（哈希集合）

解法二：快慢指针

题目

解法一：记录遍历过的结点（哈希集合）

typedef struct hashSetListNode
{
    void* val;
    struct hashSetListNode* next;
} hashSetListNodeType;
 
typedef struct hashSet
{
    hashSetListNodeType** bucket;
    uint32_t size;
} hashSetType;
 
hashSetType* hashSetInit(uint32_t size)
{
    hashSetType* hashSet = malloc(sizeof(*hashSet));
    hashSet->bucket = calloc(size, sizeof(*hashSet->bucket));
    hashSet->size = size;
    return hashSet;
}
 
// FNV-1a
uint32_t hash(const uint8_t* data, uint32_t len)
{
    uint32_t hash = 0x811c9dc5;
    for (int i = 0; i < len; i++)
    {
        hash ^= data[i];
        hash *= 0x01000193;
    }
    return hash;
}
 
void hashSetInsert(hashSetType* hashSet, void* val)
{
    uint32_t index = hash((uint8_t*)&val, sizeof(val)) % hashSet->size;
    hashSetListNodeType* newNode = malloc(sizeof(*newNode));
    newNode->val = val;
    newNode->next = hashSet->bucket[index];
    hashSet->bucket[index] = newNode;
}
 
bool hashSetFind(hashSetType* hashSet, void* val)
{
    uint32_t index = hash((uint8_t*)&val, sizeof(val)) % hashSet->size;
    hashSetListNodeType* curNode = hashSet->bucket[index];
    while (curNode)
    {
        if (curNode->val == val)
            return true;
        curNode = curNode->next;
    }
    return false;
}
 
void hashSetFree(hashSetType* hashSet)
{
    for (int i = 0; i < hashSet->size; i++)
    {
        hashSetListNodeType* freeNode = hashSet->bucket[i];
        while (freeNode)
        {
            hashSetListNodeType* nextNode = freeNode->next;
            free(freeNode);
            freeNode = nextNode;
        }
    }
    free(hashSet->bucket);
    free(hashSet);
}
 
bool check(struct ListNode* head)
{
    hashSetType* hashSet = hashSetInit(512);
    struct ListNode* curNode = head;
    bool is = false;
    while (curNode)
    {
        if (hashSetFind(hashSet, curNode))
        {
            is = true;
            break;
        }
        hashSetInsert(hashSet, curNode);
        curNode = curNode->next;
    }
    hashSetFree(hashSet);
    return is;
}
 
bool hasCycle(struct ListNode* head)
{
    return check(head);
}

解法二：快慢指针

bool check(struct ListNode* head)
{
    struct ListNode* fast = head;
    struct ListNode* slow = head;
    while (fast && fast->next)
    {
        fast = fast->next->next;
        slow = slow->next;
        if (fast == slow)
            return true;
    }
    return false;
}

bool hasCycle(struct ListNode* head)
{
    return check(head);
}