Add linked-list-cycle-ii solution

Author: imajinyun

src/leetcode/LinkedListCycleII.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode;
+
+use leetcode\util\ListNode;
+
+class LinkedListCycleII
+{
+    public static function detectCycle(?ListNode $head): ?ListNode
+    {
+        if (!$head) {
+            return null;
+        }
+        $slow = $fast = $head;
+        while ($fast->next && $fast->next->next) {
+            $slow = $slow->next;
+            $fast = $fast->next->next;
+            if ($slow === $fast) {
+                $curr = $head;
+                while ($curr !== $slow) {
+                    $curr = $curr->next;
+                    $slow = $slow->next;
+                }
+                return $slow;
+            }
+        }
+
+        return null;
+    }
+}

tests/leetcode/LinkedListCycleIITest.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode\tests;
+
+use leetcode\LinkedListCycleII;
+use PHPUnit\Framework\TestCase;
+use leetcode\util\ListNode;
+
+class LinkedListCycleIITest extends TestCase
+{
+    public static function testDetectCycle(): void
+    {
+        $node1 = new ListNode(3, new ListNode(2, new ListNode(0, new ListNode(-4))));
+        $list1 = LinkedListCycleII::detectCycle($node1);
+        self::assertSame([], ListNode::toArray($list1));
+
+        $node2 = new ListNode(1, new ListNode(2));
+        $list2 = LinkedListCycleII::detectCycle($node2);
+        self::assertSame([], ListNode::toArray($list2));
+
+        $node3 = new ListNode(1);
+        $list3 = LinkedListCycleII::detectCycle($node3);
+        self::assertSame([], ListNode::toArray($list3));
+    }
+}