Add Solution2.java to problems 0025

Author: huaxu1024

solution/0025.Reverse Nodes in k-Group/Solution2.java

@@ -0,0 +1,35 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+
+    public ListNode reverseKGroup(ListNode head, int k) {
+        if (k == 1) return head;
+        ListNode res = new ListNode(0);
+        ListNode slow = head, fast = head, index = res;
+        int i = 1;
+        while (fast != null) {
+            ListNode temp = fast.next;
+            if (i ++ % k == 0) {
+                fast.next = null;
+                ListNode zou = slow;
+                while (slow != null) {
+                    ListNode itme = slow.next;
+                    slow.next = index.next;
+                    index.next = slow;
+                    slow = itme;
+                }
+                index = zou;
+                slow = temp;
+            }
+            fast = temp;
+        }
+        index.next = slow;
+        return res.next;
+    }
+}