Heap

basic operation

• import heapq
• push heapq.heappush(heap, item)
• pop heapq.heappop(heap)

pattern

• store all items in array(max need to start -x)
• then pop within k times to find max kth or min kth

重点是搞明白heap需要按照什么key来排序,再搞明白如何push进heap的order(如何优化时间复杂度)