Update Reversed Linked List

Author: tech-cow

README.md

@@ -16,4 +16,5 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |  141  | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/#/description) | [Python](./linkedlist/LinkedListCycle.py) | _O(n)_ | _O(1)_ | Easy |CC189| Two Pointers|
 |160|[Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists) | [Python](./linkedlist/IntersectionOfTwoLinkedLists.py) | _O(n)_| _O(1)_  | Easy || |
 |203|[Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/#/description) | [Python](./linkedlist/RemoveLinkedListElements.py) | _O(n)_| _O(1)_  | Easy || |
+|206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/#/description) | [Python](./linkedlist/ReverseLinkedList.py) | _O(n)_| _O(1)_  | Easy |CC189| [Video Tutorial](https://www.youtube.com/watch?v=sYcOK51hl-A&t=681s) |
 |234|[Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/) | [Python](./linkedlist/palindrome.py) | _O(n)_| _O(1)_  | Easy |CC189| Two Pointers|

linkedlist/ReverseLinkedList.py

@@ -0,0 +1,23 @@
+class Solution(object):
+    def reverseList(self, head):
+        """
+        :type head: ListNode
+        :rtype: ListNode
+        """
+        cur = head
+        prev = None
+
+        while cur:
+            #设置一个next用来保存之后所有的链表链接，否则改了cur.next以后，
+            #第一个node就和之后的链表失联了
+            next = cur.next
+            #将cur的指针指向prev，也就是Null
+            cur.next = prev
+            #跟换prev的reference到cur，然后之后可以通过指针reference到这个prev
+            #的Node
+            prev = cur
+            #跟换cur到next,也就是之前为防止数据丢失而保存的reference
+            cur = next
+        #当list遍历到最后，把头reference到最后面一个node
+        head = prev
+        return head