Create Reverse Nodes in k-Group.cpp

Author: daizhenyang

Reverse Nodes in k-Group.cpp

@@ -0,0 +1,43 @@
+//solve by recursion
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode *reverse(ListNode *head)
+    {
+        ListNode *ptr=head,*tmp=NULL;
+        while (ptr)
+        {
+            ListNode *nxt=ptr->next;
+            ptr->next=tmp;
+            tmp=ptr;
+            ptr=nxt;
+        }
+        return tmp;
+    }
+    ListNode *reverseKGroup(ListNode *head, int k) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        if (head==NULL)return head;
+        ListNode *ptr=head;
+        int c=k;
+        while (--c&&ptr)
+        {
+            ptr=ptr->next;
+        }
+        if (!ptr)return head;
+        ListNode *nxt=ptr->next,*tmp=head;
+        ptr->next=NULL;
+        head=reverse(head);
+        tmp->next=reverseKGroup(nxt,k);
+        return head;
+        
+    }
+};