Merge pull request #1399 from fmtvar/0019

添加 (0019.删除链表的倒数第N个节点.md)：PHP版本

problems/0019.删除链表的倒数第N个节点.md

@@ -289,6 +289,30 @@ func removeNthFromEnd(_ head: ListNode?, _ n: Int) -> ListNode? {
     return dummyHead.next
 }
 ```
+
+
+PHP:
+```php
+function removeNthFromEnd($head, $n) {
+    // 设置虚拟头节点
+    $dummyHead = new ListNode();
+    $dummyHead->next = $head;
+
+    $slow = $fast = $dummyHead;
+    while($n-- && $fast != null){
+        $fast = $fast->next;
+    }
+    // fast 再走一步，让 slow 指向删除节点的上一个节点
+    $fast = $fast->next; 
+    while ($fast != NULL) {
+        $fast = $fast->next;
+        $slow = $slow->next;
+    }
+    $slow->next = $slow->next->next;
+    return $dummyHead->next;
+    }
+```
+
 Scala:
 ```scala
 object Solution {