Remove Duplicate Letters for the Largest Result

import heapq
from collections import defaultdict
 
class Solution:
    def solve(self, values, queries):
        # Build the adjacency structure
        n = len(values)
        graph = defaultdict(list)
        for u, v in queries:
            graph[u].append(v)
 
        best = [float("inf")] * n
        heap = [(0, 0)]
        while heap:
            cost, node = heapq.heappop(heap)
            if cost > best[node]:
                continue