Merge pull request #2965 from drxlx/0025-reverse-nodes-in-k-group

Create 0025-reverse-nodes-in-k-group.swift

Author: felivalencia3

swift/0025-reverse-nodes-in-k-group.swift

@@ -0,0 +1,57 @@
+/**
+ * Question Link: https://leetcode.com/problems/reverse-nodes-in-k-group/
+ */
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     public var val: Int
+ *     public var next: ListNode?
+ *     public init() { self.val = 0; self.next = nil; }
+ *     public init(_ val: Int) { self.val = val; self.next = nil; }
+ *     public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
+ * }
+ */
+
+class ReverseKGroup {
+    func reverseKGroup(_ head: ListNode?, _ k: Int) -> ListNode? {
+        var dummy = ListNode(0, head)
+        var groupPrev: ListNode? = dummy
+
+        while true {
+            let kth = getKth(current: groupPrev, k: k)
+            if kth == nil {
+                break
+            }
+
+            let groupNext = kth?.next
+
+            var prev = kth?.next
+            var current = groupPrev?.next
+            while current !== groupNext {
+                let temp = current?.next
+                current?.next = prev
+                prev = current
+                current = temp
+            }
+
+            let temp = groupPrev?.next
+            groupPrev?.next = kth
+            groupPrev = temp
+        }
+
+        return dummy.next
+    }
+
+    func getKth(current: ListNode?, k: Int) -> ListNode? {
+        var current = current
+        var k = k
+        
+        while current != nil && k > 0 {
+            current = current?.next
+            k -= 1
+        }
+
+        return current
+    }
+}