LeetCode题解 -- 双指针(141)

Linked List Cycle

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

To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where tail connects to. If pos is -1, then there is no cycle in the linked list.

时间复杂度:O(n)
空间复杂度:O(1)

temp1一次走一步，temp2一次走两步，如果链表存在环，两指针一定会相遇

public boolean hasCycle(ListNode head) {
                
        ListNode temp1 = null;
        ListNode temp2 = null;
        
        if(head != null){
            temp1 = head;
            temp2 = head;
        }else{
            return false;
        }
        
        while(temp1 != null && temp2 != null){
            temp1 = temp1.next;
            temp2 = temp2.next;
            
            if(temp2 != null){
                temp2 = temp2.next;
            }else{
                return false;
            }
            
            if(temp1 == temp2){
                return true;
            }
        }
        
        return false;
    }