Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Sign up
Appearance settings

Commit b2aba3e

Browse files
committed
linked list cycle done
1 parent 4b89f45 commit b2aba3e

File tree

2 files changed

+97
-1
lines changed

2 files changed

+97
-1
lines changed
Lines changed: 73 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,73 @@
1+
package com.leetcode.linkedlists;
2+
3+
/**
4+
* Level: Medium
5+
* Link: https://leetcode.com/problems/linked-list-cycle-ii/
6+
* Description:
7+
* Given a linked list, return the node where the cycle begins. If there is no cycle, return null.
8+
*
9+
* To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in
10+
* the linked list where tail connects to. If pos is -1, then there is no cycle in the linked list.
11+
*
12+
* Note: Do not modify the linked list.
13+
*
14+
* Example 1:
15+
*
16+
* Input: head = [3,2,0,-4], pos = 1
17+
* Output: tail connects to node index 1
18+
* Explanation: There is a cycle in the linked list, where tail connects to the second node.
19+
*
20+
*
21+
* Example 2:
22+
*
23+
* Input: head = [1,2], pos = 0
24+
* Output: tail connects to node index 0
25+
* Explanation: There is a cycle in the linked list, where tail connects to the first node.
26+
*
27+
*
28+
* Example 3:
29+
*
30+
* Input: head = [1], pos = -1
31+
* Output: no cycle
32+
* Explanation: There is no cycle in the linked list.
33+
*
34+
* Follow-up:
35+
* Can you solve it without using extra space?
36+
*
37+
* @author rampatra
38+
* @since 2019年08月18日
39+
*/
40+
public class LinkedListCycleII {
41+
42+
/**
43+
* Runtime: <a href="https://leetcode.com/submissions/detail/252786957/">0 ms</a>.
44+
*
45+
* @param head
46+
* @return
47+
*/
48+
public Node detectCycle(Node head) {
49+
Node slow = head;
50+
Node fast = head;
51+
52+
while (fast != null && fast.next != null) {
53+
slow = slow.next;
54+
fast = fast.next.next;
55+
if (slow == fast) {
56+
break;
57+
}
58+
}
59+
60+
if (fast == null || fast.next == null) {
61+
return null;
62+
} else {
63+
slow = head;
64+
65+
while (slow != fast) {
66+
slow = slow.next;
67+
fast = fast.next;
68+
}
69+
70+
return slow;
71+
}
72+
}
73+
}

‎src/main/java/com/rampatra/linkedlists/DetectAndRemoveLoop.java

Lines changed: 24 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -34,6 +34,11 @@ public class DetectAndRemoveLoop {
3434
* ii. Now, move both slow and fast pointer at same pace and where they meet is the starting point of the loop.
3535
* iii. Lastly, to remove the loop make the next of the node (before the starting point of loop) to null.
3636
*
37+
* Proof for Floyd's Cycle Detection: Consider a cyclic list and imagine the slow and fast pointers are two runners
38+
* racing around a circle track. The fast runner will eventually meet the slow runner. Why? Consider this case -
39+
* The fast runner is just one step behind the slow runner. In the next iteration, they both increment one and two
40+
* steps respectively and meet each other.
41+
*
3742
* @param list
3843
* @param <E>
3944
* @return {@code true} if loop exists {@code false} otherwise.
@@ -58,7 +63,7 @@ public static <E extends Comparable<E>> boolean detectAndRemoveLoop(SingleLinked
5863
while (true) {
5964
slow = slow.next;
6065
fast = fast.next;
61-
if (slow.next == fast.next) {
66+
if (slow == fast) {
6267
fast.next = null;
6368
break;
6469
}
@@ -78,5 +83,23 @@ public static void main(String[] args) {
7883
linkedList.getNode(4).next = linkedList.getNode(2);
7984
System.out.println(detectAndRemoveLoop(linkedList));
8085
linkedList.printList();
86+
87+
linkedList = new SingleLinkedList<>();
88+
linkedList.add(0);
89+
linkedList.add(1);
90+
linkedList.getNode(1).next = linkedList.getNode(0);
91+
System.out.println(detectAndRemoveLoop(linkedList));
92+
linkedList.printList();
93+
94+
linkedList = new SingleLinkedList<>();
95+
linkedList.add(0);
96+
System.out.println(detectAndRemoveLoop(linkedList));
97+
linkedList.printList();
98+
99+
linkedList = new SingleLinkedList<>();
100+
linkedList.add(0);
101+
linkedList.getNode(0).next = linkedList.getNode(0);
102+
System.out.println(detectAndRemoveLoop(linkedList));
103+
linkedList.printList();
81104
}
82105
}

0 commit comments

Comments
(0)

AltStyle によって変換されたページ (->オリジナル) /