23 Merge k Sorted List solution

Author: dipti95

typescript/23-Merge-k-Sorted-Lists.ts

@@ -0,0 +1,52 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function mergeKLists(lists: Array<ListNode | null>): ListNode | null {
+  if (lists.length === 0) return null
+
+  while (lists.length > 1) {
+    let resultList = []
+
+    for (let i = 0; i < lists.length; i += 2) {
+      let list1 = lists[i]
+      let list2
+      if (i + 1 > lists.length) list2 = null
+      else list2 = lists[i + 1]
+      resultList.push(mergeList(list1, list2))
+    }
+
+    lists = resultList
+  }
+  return lists[0] || null
+}
+
+function mergeList(
+  list1: ListNode | null,
+  list2: ListNode | null
+): ListNode | null {
+  let dummyNode: ListNode | null = new ListNode()
+  let tail = dummyNode
+
+  while (list1 && list2) {
+    if (list1.val < list2.val) {
+      tail.next = list1
+      list1 = list1.next
+    } else {
+      tail.next = list2
+      list2 = list2.next
+    }
+    tail = tail.next
+  }
+  tail.next = list1 || list2
+
+  return dummyNode.next
+}