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

Author: Krishnal Ciccolella

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;
+}