Create 92. Reverse Linked List II.md

solutions/92. Reverse Linked List II.md

@@ -0,0 +1,32 @@
+# [92. Reverse Linked List II](https://leetcode.com/problems/reverse-linked-list-ii/)
+# 思路
+首先还是开辟一个真正的头结点real_head, 其next指针指向head。然后向后移动`m - 1`步到达需要翻转的第一个节点的前一个节点，记为pre，如果按照下面的例子的话
+pre就指向1，然后我们翻转pre后面的`n-m`个节点即可。
+```
+Input: 1->2->3->4->5->NULL, m = 2, n = 4
+Output: 1->4->3->2->5->NULL
+```
+
+# C++
+``` C++
+class Solution {
+public:
+    ListNode* reverseBetween(ListNode* head, int m, int n) {
+        ListNode *real_head = new ListNode(0);
+        real_head -> next = head;
+        ListNode *p, *pre = real_head, *tmp;
+        n -= m;
+        while(--m) pre = pre -> next;
+        p = pre -> next;
+        
+        // reverse n-m nodes
+        while(n--){
+            tmp = p -> next;
+            p -> next = tmp -> next;
+            tmp -> next = pre -> next;
+            pre -> next = tmp;   
+        }
+        return real_head -> next;
+    }
+};
+```