merged k sorted lists

Author: eunhwa99

merge-k-sorted-lists/eunhwa99.java

@@ -0,0 +1,35 @@
+import java.util.PriorityQueue;
+
+/**
+ * Definition for singly-linked list. public class ListNode { int val; ListNode next; ListNode() {}
+ * ListNode(int val) { this.val = val; } ListNode(int val, ListNode next) { this.val = val;
+ * this.next = next; } }
+ */
+
+// TC : PQ -> O(NlogN)
+  // SC: Linked list -> O(N)
+class Solution {
+
+  public ListNode mergeKLists(ListNode[] lists) {
+    if (lists == null || lists.length == 0) {
+      return null;
+    }
+    PriorityQueue<Integer> pq = new PriorityQueue<>();
+
+    for (int i = 0; i < lists.length; i++) {
+      while (lists[i] != null) {
+        pq.add(lists[i].val);
+        lists[i] = lists[i].next;
+      }
+    }
+    ListNode dummy = new ListNode(0);
+    ListNode current = dummy;
+    while (!pq.isEmpty()) {
+      current.next = new ListNode(pq.poll());
+      current = current.next;
+    }
+
+    return dummy.next;
+  }
+}
+