#leetcode#Linked List Cycle

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1、題目

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

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

2、思路

設定兩個指標，一個每次走一步，另一個每次走兩步。走兩步的一定會追上走一步的。

3、代碼

bool hasCycle(ListNode *head)     {        bool cycle = false;        if(head==NULL)        {            return false;        }        ListNode *low_cursor = head;        if(head->next==NULL)        {            return false;        }        ListNode *fast_cursor = head->next;                                                                                                                                             while(fast_cursor->next != NULL)        {            if(fast_cursor==low_cursor)            {                cycle = true;                break;            }            else            {                low_cursor = low_cursor->next;                fast_cursor = fast_cursor->next;                if(fast_cursor==low_cursor)                {                    cycle = true;                    break;                }                if(fast_cursor->next==NULL)                {                    break;                }                       else                {                    fast_cursor = fast_cursor->next;                    if(fast_cursor==low_cursor)                    {                        cycle = true;                        break;                    }                }            }             }        return cycle;        }

　　

#leetcode#Linked List Cycle