Leetcode: Linked List Cycle

最新推荐文章于 2018-10-24 20:56:37 发布

原创最新推荐文章于 2018-10-24 20:56:37 发布 · 3.2k 阅读

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#Leetcode #Linked List #Cycle

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本文将介绍一种方法来判断给定的链表中是否存在循环，并探讨如何在不使用额外空间的情况下解决此问题。

Given a linked list, determine if it has a cycle in it.

Follow up:
Can you solve it without using extra space?

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    bool hasCycle(ListNode *head) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ListNode* pfast = head;
		ListNode* pslow = head;
		do{
			if(pfast!=NULL)
				pfast=pfast->next;
			if(pfast!=NULL)
				pfast=pfast->next;
			if(pfast==NULL)
				return false;
			pslow = pslow->next;
		}while(pfast != pslow);
		return true;
    }
};