Solution for https://leetcode.com/problems/merge-k-sorted-lists

Author: g0rd1

src/main/kotlin/problems/merge_k_sorted_lists/MergeKSortedLists.kt

@@ -0,0 +1,47 @@
+package problems.merge_k_sorted_lists
+
+import java.util.*
+
+fun main() {
+    val result = Solution().mergeKLists(
+        arrayOf(
+            getListNodeFromList(listOf(1, 4, 5)),
+            getListNodeFromList(listOf(1, 3, 4)),
+            getListNodeFromList(listOf(2, 6)),
+        )
+    )
+    println(result) // 1, 1, 2, 3, 4, 4, 5, 6
+}
+
+class Solution {
+    fun mergeKLists(lists: Array<ListNode?>): ListNode? {
+        if (lists.isEmpty()) return null
+        val listNodeQueue = PriorityQueue<ListNode>(compareBy { it.`val` })
+        listNodeQueue.addAll(lists.filterNotNull())
+        if (listNodeQueue.isEmpty()) return null
+        val firstListNode = listNodeQueue.remove()
+        val result = ListNode(firstListNode.`val`)
+        if (firstListNode.next != null) listNodeQueue.add(firstListNode.next)
+        var lastListNode: ListNode = result
+        while (listNodeQueue.isNotEmpty()) {
+            val listNode = listNodeQueue.remove()
+            val newListNode = ListNode(listNode.`val`)
+            lastListNode.next = newListNode
+            lastListNode = newListNode
+            if (listNode.next != null) listNodeQueue.add(listNode.next)
+        }
+        return result
+    }
+}
+
+class ListNode(var `val`: Int) {
+    var next: ListNode? = null
+}
+
+private fun getListNodeFromList(list: List<Int>): ListNode? {
+    var result: ListNode? = null
+    for (i in list.size - 1 downTo 0) {
+        result = ListNode(list[i]).apply { next = result }
+    }
+    return result
+}