reverse_nodes_in_k-Group.cpp

Author: jakoo

reverse_nodes_in_k-Group.cpp

@@ -0,0 +1,70 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* reverseKGroup(ListNode* head, int k) {
+        if (head == nullptr || head->next == nullptr || k == 1)
+            return head;
+        
+        ListNode* one = head;
+        ListNode* oneBackup = one;
+        ListNode* two = one->next;
+        ListNode* three = two->next;
+        ListNode* nextHead = exist(one, k);
+        
+        if (nextHead)
+            head = nextHead;
+        else
+            return head;
+
+        while (1)
+        {
+            bool end = false;
+            
+            ListNode* nextHead = exist(one, 2 * k);
+            if (nextHead)
+                one->next = nextHead;
+            else
+                end = true;
+                
+            for(int i = 0; i < k - 2; ++i)
+            {
+                two->next = one;
+                one = two;
+                two = three;
+                three = three->next;
+            }
+            two->next = one;
+            
+            if (end)
+            {
+                oneBackup->next = three;
+                break;
+            }
+            
+            one = oneBackup = three;
+            two = one->next;
+            three = two->next;
+        }
+        return head;
+    }
+    
+    ListNode* exist(ListNode* head, int k)
+    {
+        for(int i = 0; i < k - 1; ++i)
+        {
+            if (head == nullptr)
+            {
+                return nullptr;
+            }
+            head = head->next;
+        }
+        return head;
+    }
+};