Create 25-reverse-nodes-in-k-group.js

Author: everthis

25-reverse-nodes-in-k-group.js

@@ -0,0 +1,30 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @param {number} k
+ * @return {ListNode}
+ */
+const reverseKGroup = function(head, k) {
+  let n = 0
+  for (let i = head; i != null; n++, i = i.next);
+  let dmy = new ListNode(0)
+  dmy.next = head
+  for (let prev = dmy, tail = head; n >= k; n -= k) {
+    for (let i = 1; i < k; i++) {
+      let next = tail.next.next
+      tail.next.next = prev.next
+      prev.next = tail.next
+      tail.next = next
+    }
+
+    prev = tail
+    tail = tail.next
+  }
+  return dmy.next
+}