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listcircle.java
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listcircle.java
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package leetcode;
import java.util.HashSet;
public class listcircle {
static class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
next = null;
}
}
public static boolean hasCycle(ListNode head) {
HashSet<ListNode> search = new HashSet<ListNode>();
int i = 0;
int j = 0;
while(head != null){
i = search.size();
search.add(head);
j = search.size();
if(i == j){
return true;
}
head = head.next;
}
return false;
}
public static boolean hasCycle1(ListNode head){
if(head == null ){
return false;
}
if(head.next == null) return false;
ListNode node1 = head;
ListNode node2 = head;
while(true){
if(node1.next == node2.next.next){
return true;
}
if(node1.next == null ) return false;
if(node2.next == null) return false;
if(node2.next.next == null) return false;
node1 = node1.next;
node2 = node2.next.next;
}
}
public static void main(String[] args){
ListNode node1 = new ListNode(1);
ListNode node2 = new ListNode(2);
node1.next = node2;
node2.next = node1;
System.out.println(hasCycle1(node1));
}
}