Maximum Score of a Node Sequence — Python

# Time:  O(|V| + |E|)
# Space: O(|V|)

import heapq


# graph
class Solution(object):
    def maximumScore(self, scores, edges):
        """
        :type scores: List[int]
        :type edges: List[List[int]]
        :rtype: int
        """
        def find_top3(scores, x, top3):
            heapq.heappush(top3, (scores[x], x))
            if len(top3) > 3:
                heapq.heappop(top3)

        top3 = [[] for _ in xrange(len(scores))]
        for a, b in edges:
            find_top3(scores, b, top3[a])
            find_top3(scores, a, top3[b])
        result = -1
        for a, b in edges:
            for _, c in top3[a]:
                if c == b:
                    continue
                for _, d in top3[b]:
                    if d == a or d == c:
                        continue
                    result = max(result, sum(scores[x] for x in (a, b, c, d)))
        return result