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HasCycle.java
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61 lines (55 loc) · 1.24 KB
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package normal;
import java.util.HashSet;
/**
* @program JavaBooks
* @description: 141.环形链表
* @author: mf
* @create: 2019/11/05 10:19
*/
/*
题目：
难度：easy
类型：链表
*/
public class HasCycle {
public static void main(String[] args) {
}
/**
* 哈希
* @param head
* @return
*/
public static boolean hasCycle(ListNode head) {
HashSet<ListNode> set = new HashSet<>();
while (head != null) {
if (set.contains(head)) {
return true;
} else {
set.add(head);
}
head = head.next;
}
return false;
}
/**
* 快慢指针
* @param head
* @return
*/
public static boolean hasCycle2(ListNode head) {
if (head != null && head.next != null) {
ListNode quick = head;
ListNode slow = head;
while (2 > 1) {
quick = quick.next;
if (quick == null) return false;
quick = quick.next;
if (quick == null) return false;
slow = slow.next;
if (slow == quick) return true;
}
} else {
return false;
}
}
}