leetcode-algorithms/src/LinkedListCycleII.java at master · anishLearnsToCode/leetcode-algorithms · GitHub

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// https://leetcode.com/problems/linked-list-cycle-ii

// T: O(n)

// S: O(1)

public class LinkedListCycleII {

public ListNode detectCycle(ListNode head) {

if (head == null) return null;

ListNode slow = head, fast = head, entry = head;

while (fast.next != null && fast.next.next != null) {

slow = slow.next;

fast = fast.next.next;

if (slow == fast) {

while (entry != slow) {

entry = entry.next;

slow = slow.next;

}

return entry;

}

return null;

}

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