merge K sorted lists hard

Author: weiy

Heap/MergeKSortedLists.py

@@ -0,0 +1,58 @@
+"""
+Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
+
+Example:
+
+Input:
+[
+  1->4->5,
+  1->3->4,
+  2->6
+]
+Output: 1->1->2->3->4->4->5->6
+
+合并 k 个有序链表。
+
+用了最小堆：
+
+把所有的链表节点入堆，然后出堆形成新的链表即可。
+
+依然依靠了内置模块，待自己书写堆。
+
+测试地址：
+https://leetcode.com/problems/merge-k-sorted-lists/description/
+
+"""
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+import heapq
+
+class Solution(object):
+    def mergeKLists(self, lists):
+        """
+        :type lists: List[ListNode]
+        :rtype: ListNode
+        """
+        a = []
+        
+        heapq.heapify(a)
+        
+        for i in lists:
+            while i:
+                heapq.heappush(a, i.val)
+                i = i.next
+        if not a:
+            return None
+        
+        root = ListNode(heapq.heappop(a))
+        head = root
+        
+        while a:
+            root.next = ListNode(heapq.heappop(a))
+            root = root.next
+        
+        return head
+