class Solution(object):
def lastStoneWeight(self, stones):
"""
:type stones: List[int]
:rtype: int
"""
max_heap = [-x for x in stones]
heapq.heapify(max_heap)
for i in xrange(len(stones)-1):
x,y = -heapq.heappop(max_heap), -heapq.heappop(max_heap)
heapq.heappush(max_heap, -abs(x-y))
return -max_heap[0]