LeetCode Linked List Cycle 解答程序
2013-10-30 10:44
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Linked List Cycle
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
错误解法。因为Cycle可能出现在Link的中间的,所以需要检查其中间Nodes。
正确解法:
更新I的O(n)算法:
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
错误解法。因为Cycle可能出现在Link的中间的,所以需要检查其中间Nodes。
bool hasCycle(ListNode *head) { // IMPORTANT: Please reset any member data you declared, as // the same Solution instance will be reused for each test case. if(head == NULL) return false; ListNode *cur = head; while(cur != NULL) { cur = cur->next; if(cur == head) return true; } return false; }
正确解法:
class Solution { public: bool find(ListNode *head, ListNode *testpNode) { ListNode *p = head; while (p != testpNode->next) { if(p == testpNode) return false; p = p->next; } return true; } bool hasCycle(ListNode *head) { // IMPORTANT: Please reset any member data you declared, as // the same Solution instance will be reused for each test case. if(head == NULL) return false; ListNode *cur = head; while(cur != NULL) { if(find(head, cur)) return true; cur = cur->next; } return false; } };
更新I的O(n)算法:
//2014-2-19 update bool hasCycle(ListNode *head) { ListNode *fast = head; ListNode *slow = head; while (fast) { slow = slow->next; fast = fast->next; if (fast) fast = fast->next; if (fast && slow == fast) return true; } return false; }
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