Add remove-nth-node-from-end-of-list solution

Author: imajinyun

src/leetcode/RemoveNthNodeFromEndOfList.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode;
+
+use leetcode\util\ListNode;
+
+class RemoveNthNodeFromEndOfList
+{
+    public static function removeNthFromEnd(?ListNode $head, int $n): ?ListNode
+    {
+        if (!$head) {
+            return null;
+        }
+        $node = new ListNode();
+        $node->next = $head;
+        $slow = $fast = $node;
+        for ($i = 1; $i <= $n + 1; $i++) {
+            $fast = $fast->next;
+        }
+        while ($fast) {
+            $slow = $slow->next;
+            $fast = $fast->next;
+        }
+        $slow->next = $slow->next->next;
+
+        return $node->next;
+    }
+
+    public static function removeNthFromEnd2(?ListNode $head, int $n): ?ListNode
+    {
+        if (!$head) {
+            return null;
+        }
+        $slow = $fast = $head;
+        for ($i = 0; $i < $n; $i++) {
+            $fast = $fast->next;
+        }
+        if (!$fast) {
+            return $head->next;
+        }
+        while ($fast->next) {
+            $slow = $slow->next;
+            $fast = $fast->next;
+        }
+        $slow->next = $slow->next->next;
+
+        return $head;
+    }
+}

tests/leetcode/RemoveNthNodeFromEndOfListTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode\tests;
+
+use PHPUnit\Framework\TestCase;
+use leetcode\RemoveNthNodeFromEndOfList;
+use leetcode\util\ListNode;
+
+class RemoveNthNodeFromEndOfListTest extends TestCase
+{
+    public function testRemoveNthFromEnd(): void
+    {
+        $node1 = new ListNode(1, new ListNode(2, new ListNode(3, new ListNode(4, new ListNode(5)))));
+        $list1 = RemoveNthNodeFromEndOfList::removeNthFromEnd($node1, 2);
+        self::assertSame([1, 2, 3, 5], ListNode::toArray($list1));
+
+        $node2 = new ListNode(1);
+        $list2 = RemoveNthNodeFromEndOfList::removeNthFromEnd($node2, 1);
+        self::assertSame([], ListNode::toArray($list2));
+
+        $node3 = new ListNode(1, new ListNode(2));
+        $list3 = RemoveNthNodeFromEndOfList::removeNthFromEnd($node3, 1);
+        self::assertSame([1], ListNode::toArray($list3));
+    }
+
+    public function testRemoveNthFromEnd2(): void
+    {
+        $node1 = new ListNode(1, new ListNode(2, new ListNode(3, new ListNode(4, new ListNode(5)))));
+        $list1 = RemoveNthNodeFromEndOfList::removeNthFromEnd2($node1, 2);
+        self::assertSame([1, 2, 3, 5], ListNode::toArray($list1));
+
+        $node2 = new ListNode(1);
+        $list2 = RemoveNthNodeFromEndOfList::removeNthFromEnd2($node2, 1);
+        self::assertSame([], ListNode::toArray($list2));
+
+        $node3 = new ListNode(1, new ListNode(2));
+        $list3 = RemoveNthNodeFromEndOfList::removeNthFromEnd2($node3, 1);
+        self::assertSame([1], ListNode::toArray($list3));
+    }
+}