Create 25-Reverse-Nodes-in-K-Group.js

javascript/25-Reverse-Nodes-in-K-Group.js

@@ -0,0 +1,51 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ * this.val = (val===undefined ? 0 : val)
+ * this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @param {number} k
+ * @return {ListNode}
+ */
+var reverseKGroup = function(head, k) {
+ let dummy = new ListNode(0, head);
+ let groupPrev = dummy;
+
+ while (true) {
+ let kth = getKth(groupPrev, k);
+ if (!kth) {
+ break;
+ }
+
+ let groupNext = kth.next;
+
+ // reverse group
+ let prev = kth.next;
+ let curr = groupPrev.next;
+
+ while (curr !== groupNext) {
+ let temp = curr.next;
+ curr.next = prev;
+ prev = curr;
+ curr = temp; 
+ }
+
+ let temp = groupPrev.next;
+ groupPrev.next = kth;
+ groupPrev = temp;
+ }
+
+ return dummy.next;
+};
+
+function getKth(curr, k) {
+ while (curr && k > 0) {
+ curr = curr.next;
+ k -= 1;
+ }
+
+ return curr;
+}