Create Merge k Sorted (Linked) Lists - Leetcode 23.py

Author: gahogg

Merge k Sorted (Linked) Lists - Leetcode 23.py

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+import heapq
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def mergeKLists(self, lists: List[Optional[ListNode]]) -> Optional[ListNode]:
+        heap = []
+        for i, node in enumerate(lists):
+            if node:
+                heapq.heappush(heap, (node.val, i, node))
+        
+        D = ListNode()
+        cur = D
+        
+        # n log k
+        while heap:
+            val, i, node = heapq.heappop(heap)
+            cur.next = node
+            cur = node
+            node = node.next
+            if node:
+                heapq.heappush(heap, (node.val, i, node))
+        
+        return D.next
+        # Time: O(N log K)
+        # Space: O(K)