algorithm/Week_01/id_124/LeetCode_142_124.java at master · feixiangcode/algorithm · GitHub

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import common.ListNode;

import java.util.HashSet;

import java.util.Set;

public class DetectCycle {

public ListNode detectCycle(ListNode head) {

if (head == null || head.next == null) {

return null;

}

ListNode fast = head;

ListNode slow = head;

while (fast != null) {

if (fast.next == null) {

return null;

}

fast = fast.next.next;

slow = slow.next;

if (fast == slow) {

fast = head;

while (fast != slow) {

fast = fast.next;

slow = slow.next;

}

break;

}

return fast;

}

public ListNode detectCycleByMap(ListNode head) {

Set<ListNode> set = new HashSet<>();

while (head != null) {

if (set.contains(head)) {

return head;

} else {

set.add(head);

}

head = head.next;

}

return null;

}

public static void main(String[] args) {

}

algorithm/Week_01/id_124/LeetCode_142_124.java at master · feixiangcode/algorithm · GitHub

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