make solution of Reverse Linked List II easy to understand

Author: P-ppc

algorithms/ReverseLinkedListII/README.md

@@ -1,37 +1,2 @@
 # Reverse Linked List II
-We can solve this problem by dummy node, but why the solution like below often get internal error?
-```python
-# Definition for singly-linked list.
-# class ListNode(object):
-#     def __init__(self, x):
-#         self.val = x
-#         self.next = None
-
-class Solution(object):
-    def reverseBetween(self, head, m, n):
-        """
-        :type head: ListNode
-        :type m: int
-        :type n: int
-        :rtype: ListNode
-        """
-        dummy = ListNode(-1)
-        dummy.next = head
-        cur = dummy
-        pre = None
-        i = 0
-        
-        while i < m:
-            pre = cur
-            cur = cur.next
-            i += 1
-          
-        while i < n:
-            temp = pre.next
-            pre.next = cur.next
-            cur.next = cur.next.next
-            pre.next.next = temp
-            i += 1
-        
-        return dummy.next
-```
+We can solve this problem by dummy node

algorithms/ReverseLinkedListII/Solution.java

@@ -26,6 +26,7 @@ public ListNode reverseBetween(ListNode head, int m, int n) {
             cur = next;
         }
 
+        // the tail of reverse
         pre.next.next = cur;
         pre.next = reverse;
         return dummy.next;

algorithms/ReverseLinkedListII/solution.js

@@ -29,7 +29,7 @@ var reverseBetween = function(head, m, n) {
         reverse = cur
         cur = next
     }
-    
+    // the tail of reverse
     pre.next.next = cur
     pre.next = reverse
 

algorithms/ReverseLinkedListII/solution.py

@@ -30,7 +30,7 @@ def reverseBetween(self, head, m, n):
             cur.next = reverse
             reverse = cur
             cur = nxt
-            
+        # the tail of reverse
         pre.next.next = cur
         pre.next = reverse