141. Linked List Cycle 环形链表

题目

---

代码部分一（1ms 77.01%）

public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head == null)
            return false;
        ListNode s = head;
        ListNode f = head.next;
        while(f != null){
            if(f == s){
                return true;
            }
            
            if(f.next == null)
                return false;
            f = f.next.next;
            s = s.next;
        }
        return false;
    }
}

代码部分二（16ms 4.12%）

public class Solution {
    public boolean hasCycle(ListNode head) {
        Set<ListNode> set = new HashSet<>();
        while(head != null){
            if(set.contains(head))
                return true;
            else
                set.add(head);
            head = head.next;
        }
        return false;
    }
}

代码部分三（1ms 77.81%)

public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head == null || head.next == null) return false;
        
        ListNode slow = head;
        ListNode fast = head.next;
        
        while(fast != null && fast.next != null){
            if(fast == slow) return true;
            
            slow = slow.next;
            fast = fast.next.next;
            
        }
        
        return false;
    }
}

代码部分四（0ms 99.99%）

public class Solution {
    public boolean hasCycle(ListNode head) {
        if(head == null || head.next == null) return false;
        
        ListNode slow = head;
        ListNode fast = head.next;
        int len = 1;
        
        while(slow != fast){
            if(fast == null || fast.next == null) return false;
            
            slow = slow.next;
            fast = fast.next.next;
            len++;
        }
        return true;
    }
}