如何使用 Python 堆实现密码学算法？

import heapq

# 构造邻接表表示的图
graph = {
    'start': {'A': 6, 'B': 2},
    'A': {'finish': 1},
    'B': {'A': 3, 'finish': 5},
    'finish': {}
}

# 构造节点的开销表
infinity = float('inf')
costs = {
    'A': 6,
    'B': 2,
    'finish': infinity
}

# 构造节点的父节点表
parents = {
    'A': 'start',
    'B': 'start',
    'finish': None
}

# 构造一个空堆
heap = []

# 把起点加入堆中
heapq.heappush(heap, (0, 'start'))

# 开始迭代
while heap:
    # 弹出堆中成本最小的节点
    (cost, node) = heapq.heappop(heap)
    # 如果当前节点已经被处理过，直接跳过
    if cost > costs[node]:
        continue
    # 遍历当前节点的邻居节点
    for neighbor, neighbor_cost in graph[node].items():
        # 计算从起点到当前节点的成本加上当前节点到邻居节点的成本
        new_cost = cost + neighbor_cost
        # 如果发现一条更短的路径，更新开销表和父节点表
        if new_cost < costs[neighbor]:
            costs[neighbor] = new_cost
            parents[neighbor] = node
            # 把邻居节点加入堆中，为下一轮迭代做准备
            heapq.heappush(heap, (new_cost, neighbor))

# 打印结果
print(costs)
print(parents)