19 still confused

Author: tech-cow

README.md

@@ -36,3 +36,4 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |83|[Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list/#/description)| [Python](./linkedlist/deleteDuplicates.py) | _O(n)_| _O(1)_  | Easy | ||
 |148|[Sort List](https://leetcode.com/problems/sort-list/#/description)| [Python](./linkedlist/sortList.py) | _O(nlogn)_| _O(1)_  | Medium | ||
 |61|[Rotate List](https://leetcode.com/problems/rotate-list/#/description)| [Python](./linkedlist/rotateRight.py) | _O(n)_| _O(1)_  | Medium | ||
+|19|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/#/description)| [Python](./linkedlist/removeNthFromEnd.py) | _O(n)_| _O(1)_  | Medium | ||

linkedlist/removeNthFromEnd.py

@@ -0,0 +1,22 @@
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution(object):
+    def removeNthFromEnd(self, head, n):
+        slow = fast = head
+        for _ in xrange(n):
+            fast = fast.next
+
+        # 我本来的代码没有15-16行，可以给我解释下这个edge case干了什么么
+        # 论坛里面都设置了dummynode，这题为什么要设置dummynode
+        # 先去玩狼人杀，回来继续研究
+        if not fast:
+            return head.next
+        while fast.next:
+            slow = slow.next
+            fast = fast.next
+        slow.next = slow.next.next
+        return head