Add Solution.java to problems 0023

Author: huaxu1024

solution/0023.Merge k Sorted Lists/Solution2.java

@@ -0,0 +1,37 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+import java.util.*;
+
+class Solution {
+    public ListNode mergeKLists(ListNode[] lists) {
+        ListNode res = new ListNode(0), move = res;
+        PriorityQueue<ListNode> queue = new PriorityQueue<>(3, new Comparator<ListNode>() {
+            public int compare(ListNode o1, ListNode o2) {
+                return o1.val - o2.val;
+            }
+        });
+
+        for (ListNode node : lists) {
+            if (node != null) {
+                queue.offer(node);
+            }
+        }
+
+        while (!queue.isEmpty()) {
+            ListNode poll = queue.poll();
+            move.next = poll;
+            move = move.next;
+
+            if (poll.next != null) {
+                queue.offer(poll.next);
+            }
+        }
+        return res.next;
+    }
+}