目錄

題目

解法一：哈希

解法二：快慢指針

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題目

解法一：哈希

struct node
{struct ListNode* val;struct node* next;
};struct hashSet
{struct node** bucket;int size;
};struct hashSet* hashSetInit(int size)
{struct hashSet* hashSet = malloc(sizeof(*hashSet));hashSet->bucket = calloc(size, sizeof(*hashSet->bucket));hashSet->size = size;return hashSet;
}long long hash(struct hashSet* hashSet, struct ListNode* val)
{return ((long long)val >> 7) % hashSet->size;
}void hashSetInsert(struct hashSet* hashSet, struct ListNode* val)
{long long index = hash(hashSet, val);struct node* newNode = malloc(sizeof(*newNode));newNode->val = val;newNode->next = hashSet->bucket[index];hashSet->bucket[index] = newNode;
}bool hashSetFind(struct hashSet* hashSet, struct ListNode* val)
{long long index = hash(hashSet, val);struct node* curNode = hashSet->bucket[index];while (curNode){if (curNode->val == val)return true;curNode = curNode->next;}return false;
}void hashSetFree(struct hashSet* hashSet)
{for (int i = 0; i < hashSet->size; i++){struct node* freeNode = hashSet->bucket[i];while (freeNode){struct node* nextNode = freeNode->next;free(freeNode);freeNode = nextNode;}}free(hashSet->bucket);free(hashSet);
}bool isCycle(struct ListNode* head)
{struct hashSet* 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 isCycle(head);
}

解法二：快慢指針

bool isCycle(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 isCycle(head);
}