206_Reverse_Linked_List

Author: qiyuangong

README.md

@@ -70,6 +70,7 @@
 | 186 | [Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/) ♥| [Python](https://github.com/qiyuangong/leetcode/blob/master/python/186_Reverse_Words_in_a_String_II.py) | Reverse all and reverse each words |
 | 198 | [House Robber](https://leetcode.com/problems/house-robber/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/198_House_Robber.py) | f(k) = max(f(k – 2) + num[k], f(k – 1)), O(n) and O(1) |
 | 200 | [Number of Islands](https://leetcode.com/problems/number-of-islands/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/200_Number_of_Islands.py) | 1. Quick union find, O(nlogn) and O(n^2)<br>2. BFS with marks, O(n^2) and O(1) |
+| 206 | [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/206_Reverse_Linked_List.py) | 1. Stack, O(n) and O(n)<br>2. Traverse on prev and curr, then curr.next = prev, O(n) and O(1)<br>3. Recursion, O(n) and O(1) | 
 | 213 | [House Robber II](https://leetcode.com/problems/house-robber-ii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/213_House_Robber_II.py) | f(k) = max(f(k – 2) + num[k], max(dp[0~ls-2],dp[1~ls-1], O(n) and O(1)|
 | 217 | [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/217_Contains_Duplicate.py) | 1. Set and compare length<br>2. Sort and check i,i +1|
 | 219 | [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/219_Contains_Duplicate_II.py) | 1. Brute force<br> 2. Maintenance a set that contains previous k numbers, and check if curr in set |

python/206_Reverse_Linked_List.py

@@ -4,6 +4,7 @@
 #         self.val = x
 #         self.next = None
 
+
 class Solution(object):
     # def reverseList(self, head):
     #     """
@@ -60,14 +61,11 @@ class Solution(object):
     #     return prev
 
     def reverseList(self, head):
+        # recursion
         # simple recursively without extra space
         if head is None or head.next is None:
             return head
         p = self.reverseList(head.next)
         head.next.next = head
         head.next = None
         return p
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