Create 25-Reverse-Nodes-in-k-Group.cs

csharp/25-Reverse-Nodes-in-k-Group.cs

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+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ * public int val;
+ * public ListNode next;
+ * public ListNode(int val=0, ListNode next=null) {
+ * this.val = val;
+ * this.next = next;
+ * }
+ * }
+ */
+public class Solution
+{
+ public ListNode ReverseKGroup(ListNode head, int k)
+ {
+ var dummy = new ListNode(0, head);
+ var groupPrev = dummy;
+ var groupNext = dummy;
+
+ while (true)
+ {
+ var kth = getKth(groupPrev, k);
+ if (kth == null)
+ break;
+
+ groupNext = kth.next;
+
+ // reverse group
+ var prev = kth.next;
+ var curr = groupPrev.next;
+
+ while (curr != groupNext)
+ {
+ var temp = curr.next;
+ curr.next = prev;
+ prev = curr;
+ curr = temp;
+ }
+
+ var tmp = groupPrev.next;
+ groupPrev.next = kth;
+ groupPrev = tmp;
+ }
+
+ return dummy.next;
+ }
+
+ private ListNode getKth(ListNode curr, int k)
+ {
+ while (curr != null && k > 0)
+ {
+ curr = curr.next;
+ k -= 1;
+ }
+
+ return curr;
+ }
+}