25. Reverse Nodes in k-Group

Author: Kai Yang

25.ReverseNodesInKGroup.Test.cs

@@ -0,0 +1,34 @@
+using System;
+using Newtonsoft.Json;
+using NUnit.Framework;
+
+[TestFixture]
+public class TestClass : TestClassBase
+{
+    [TestCase(10, 10, 1000)]
+    public void TestMethod(int maxLength, int maxValue, int repeatTimes)
+    {
+        Repeat(repeatTimes, () =>
+        {
+            var nums = GenerateIntegerArray(maxLength, maxValue);
+            var original = JsonConvert.SerializeObject(nums);
+            var head = ListNode.GetHead(nums);
+            var k = nums.Length == 0 ? 0 : Random.Next(1, nums.Length + 1);
+            ReverseKGroup(nums, k);
+            var result = new Solution().ReverseKGroup(head, k);
+            Assert.AreEqual(JsonConvert.SerializeObject(nums), ListNode.Serialize(result),
+                string.Format("{0}. {1}.", original, k));
+        });
+    }
+
+    private void ReverseKGroup(int[] nums, int k)
+    {
+        if (k < 2) return;
+        var i = 0;
+        while (i + k <= nums.Length)
+        {
+            Array.Reverse(nums, i, k);
+            i += k;
+        }
+    }
+}

25.ReverseNodesInKGroup.cs

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+public class Solution {
+    public ListNode ReverseKGroup(ListNode head, int k) {
+        if (k < 2) return head;
+        ListNode newHead = null;
+        ListNode newTail = null;
+        var current = head;
+        while (current != null)
+        {
+            ListNode segmentHead = null;
+            ListNode segmentTail = null;
+            var count = 0;
+            while (current != null && count < k)
+            {
+                if (segmentHead == null) segmentHead = current;
+                segmentTail = current;
+                current = current.next;
+                ++count;
+            }
+            segmentTail.next = null;
+            if (count == k)
+            {
+                segmentTail = segmentHead;
+                segmentHead = ReverseList(segmentHead);
+            }
+            if (newHead == null)
+            {
+                newHead = segmentHead;
+                newTail = segmentTail;
+            }
+            else
+            {
+                newTail.next = segmentHead;
+                newTail = segmentTail;
+            }
+        }
+        return newHead;
+    }
+
+    private ListNode ReverseList(ListNode head)
+    {
+        var current = head;
+        head = null;
+        while (current != null)
+        {
+            var next = current.next;
+            current.next = head;
+            head = current;
+            current = next;
+        }
+        return head;
+    }
+}