feat: merge-k-sorted-lists

Author: minji-go

merge-k-sorted-lists/minji-go.java

@@ -0,0 +1,51 @@
+/**
+ * <a href="https://leetcode.com/problems/https://leetcode.com/problems/merge-k-sorted-lists/">week10-5. merge-k-sorted-lists</a>
+ * <li>Description: Merge all the linked-lists into one sorted linked-list          </li>
+ * <li>Topics: Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort   </li>
+ * <li>Time Complexity: O(NlogK), Runtime 1ms   </li>
+ * <li>Space Complexity: O(K), Memory 44.7MB   </li>
+ */
+class Solution {
+    public ListNode mergeKLists(ListNode[] lists) {
+        if (lists == null || lists.length == 0) {
+            return null;
+        }
+        return mergeKLists(lists, 0, lists.length - 1);
+    }
+
+    private ListNode mergeKLists(ListNode[] lists, int start, int end) {
+        if (start == end) {
+            return lists[start];
+        }
+
+        int mid = (start + end) / 2;
+        ListNode node1 = mergeKLists(lists, start, mid);
+        ListNode node2 = mergeKLists(lists, mid + 1, end);
+        return mergeTwoLists(node1, node2);
+    }
+
+    private ListNode mergeTwoLists(ListNode node1, ListNode node2) {
+        ListNode dummy = new ListNode(-10_001);
+        ListNode merge = dummy;
+
+        while (node1 != null && node2 != null) {
+            if (node1.val < node2.val) {
+                merge.next = node1;
+                merge = merge.next;
+                node1 = node1.next;
+            } else {
+                merge.next = node2;
+                merge = merge.next;
+                node2 = node2.next;
+            }
+        }
+
+        if (node1 != null && node2 == null) {
+            merge.next = node1;
+        } else {
+            merge.next = node2;
+        }
+
+        return dummy.next;
+    }
+}