add solution for leetcode 19

Author: swiftwind0405

README.md

@@ -393,7 +393,7 @@ LeetCode
 |22|[Generate Parentheses](https://leetcode.com/problems/generate-parentheses/)| [js](./algorithms/generateParentheses/generateParentheses.js) |Medium|
 |21|[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| |Easy|
 |20|[Valid Parentheses](https://leetcode.com/problems/valid-parentheses/)| |Easy|
-|19|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)| |Easy|
+|19|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)| [js](./algorithms/removeNthNodeFromEndOfList/removeNthNodeFromEndOfList.js) |Easy|
 |18|[4Sum](https://leetcode.com/problems/4sum/)| |Medium|
 |17|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)| |Medium|
 |16|[3Sum Closest](https://leetcode.com/problems/3sum-closest/)| |Medium|

algorithms/removeNthNodeFromEndOfList/removeNthNodeFromEndOfList.js

@@ -0,0 +1,19 @@
+let removeNthFromEnd = function (head, n) {
+    // 添加哨兵节点
+    let dummy = new ListNode(0);
+    dummy.next = head;
+    let fast = dummy, slow = dummy;
+    // 快指针先走 n+1 步
+    while(n--) {
+        fast = fast.next;
+    }
+    // 快慢指针同时走
+    // 快指针走到最后的时候，慢指针的位置就是第N个节点的前一个节点的位置
+    while(fast && fast.next) {
+        fast = fast.next;
+        slow = slow.next;
+    }
+    // 删除这个节点
+    slow.next = slow.next.next;
+    return dummy.next;
+}