diff --git a/problems/0019.删除链表的倒数第N个节点.md b/problems/0019.删除链表的倒数第N个节点.md
index 3499ab9d..62fe4f8b 100644
--- a/problems/0019.删除链表的倒数第N个节点.md
+++ b/problems/0019.删除链表的倒数第N个节点.md
@@ -188,18 +188,20 @@ TypeScript:
 ```typescript
 function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
     let newHead: ListNode | null = new ListNode(0, head);
-    let slowNode: ListNode | null = newHead,
-        fastNode: ListNode | null = newHead;
-    for (let i = 0; i < n; i++) {
-        fastNode = fastNode.next;
+    //根据leetcode题目的定义可推断这里快慢指针均不需要定义为ListNode | null。
+    let slowNode: ListNode = newHead;
+    let fastNode: ListNode = newHead;
+
+    while(n--) {
+        fastNode = fastNode.next!; //由虚拟头节点前进n个节点时,fastNode.next可推断不为null。
     }
-    while (fastNode.next) {
+    while(fastNode.next) {  //遍历直至fastNode.next = null， 即尾部节点。 此时slowNode指向倒数第n个节点。
         fastNode = fastNode.next;
-        slowNode = slowNode.next;
+        slowNode = slowNode.next!;
     }
-    slowNode.next = slowNode.next.next;
-    return newHead.next;
-};
+    slowNode.next = slowNode.next!.next; //倒数第n个节点可推断其next节点不为空。 
+    return newHead.next; 
+}
 ```
 
 版本二（计算节点总数法）：