마지막 문제 추가

Author: jdalma

merge-k-sorted-lists/jdalma.kt

@@ -0,0 +1,130 @@
+package leetcode_study
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+import java.lang.RuntimeException
+
+class `merge-k-sorted-lists` {
+
+    data class ListNode(var `val`: Int) {
+        var next: ListNode? = null
+
+        companion object {
+            fun of(vararg `val`: Int): ListNode {
+                val dummy = ListNode(-1)
+                var prev = dummy
+                for (v in `val`) {
+                    prev.next = ListNode(v)
+                    prev = prev.next ?: throw RuntimeException()
+                }
+                return dummy.next ?: throw RuntimeException()
+            }
+        }
+    }
+
+    fun mergeKLists(lists: Array<ListNode?>): ListNode? {
+        return if (lists.isEmpty()) null
+        else if (lists.size == 1) lists.first()
+        else mergeDivideAndConquer(lists)
+    }
+
+    /**
+     * TC: O(lists.size * ListNode.size), SC: O(1)
+     */
+    private fun usingBruteForce(lists: Array<ListNode?>): ListNode? {
+        val dummy = ListNode(-1)
+        var prev = dummy
+
+        while (true) {
+            var minNode: ListNode? = null
+            var minIndex = -1
+
+            for (index in lists.indices) {
+                val curr = lists[index] ?: continue
+                if (minNode == null || curr.`val` < minNode.`val`) {
+                    minNode = curr
+                    minIndex = index
+                }
+            }
+            prev.next = minNode ?: break
+            prev = prev.next ?: throw RuntimeException()
+
+            lists[minIndex] = minNode.next
+        }
+
+        return dummy.next
+    }
+
+    /**
+     * TC: O(lists.size * ListNode.size), SC: O(1)
+     */
+    private fun mergeLists(lists: Array<ListNode?>): ListNode? {
+        fun merge(node1: ListNode?, node2: ListNode?): ListNode? {
+            val dummy = ListNode(-1)
+            var prev = dummy
+            var (n1, n2) = node1 to node2
+            while (n1 != null && n2 != null) {
+                if (n1.`val` < n2.`val`) {
+                    prev.next = n1
+                    n1 = n1.next
+                } else {
+                    prev.next = n2
+                    n2 = n2.next
+                }
+                prev.next?.let { prev = it }
+            }
+            prev.next = n1 ?: n2
+            return dummy.next
+        }
+        for (index in 1 until lists.size) {
+            lists[0] = merge(lists[0], lists[index])
+        }
+        return lists[0]
+    }
+
+    /**
+     * TC: O(lists.size * ListNode.size), SC: O(lists.size)
+     */
+    private fun mergeDivideAndConquer(lists: Array<ListNode?>): ListNode? {
+        fun merge(node1: ListNode?, node2: ListNode?): ListNode? {
+            val dummy = ListNode(-1)
+            var prev = dummy
+            var (n1, n2) = node1 to node2
+            while (n1 != null && n2 != null) {
+                if (n1.`val` < n2.`val`) {
+                    prev.next = n1
+                    n1 = n1.next
+                } else {
+                    prev.next = n2
+                    n2 = n2.next
+                }
+                prev.next?.let { prev = it }
+            }
+            prev.next = n1 ?: n2
+            return dummy.next
+        }
+
+        fun divideAndConquer(lists: Array<ListNode?>, s: Int, e: Int): ListNode? {
+            if (s > e) return null
+            else if (s == e) return lists[s]
+
+            val mid = (s + e) / 2
+            val left = divideAndConquer(lists, s, mid)
+            val right = divideAndConquer(lists, mid + 1, e)
+            return merge(left, right)
+        }
+
+        return divideAndConquer(lists, 0, lists.size - 1)
+    }
+
+    @Test
+    fun `전달받은 노드들을 정렬하고 병합된 결과를 반환한다`() {
+        mergeKLists(
+            arrayOf(
+                ListNode.of(1,4,5),
+                ListNode.of(1,3,4),
+                ListNode.of(2,6)
+            )
+        ) shouldBe ListNode.of(1,1,2,3,4,4,5,6)
+    }
+}