如何在不使用Python语言中的NetworkX函数的情况下编写计算图的距离矩阵的函数distance_matrix？

import heapq

def dijkstra(graph, start):
    queue = []
    heapq.heappush(queue, (0, start))
    distances = {node: float('inf') for node in graph}
    distances[start] = 0
    while queue:
        current_distance, current_node = heapq.heappop(queue)
        if current_distance > distances[current_node]:
            continue
        for neighbor, weight in graph[current_node].items():
            distance = current_distance + weight
            if distance < distances[neighbor]:
                distances[neighbor] = distance
                heapq.heappush(queue, (distance, neighbor))
    return distances

def distance_matrix(graph):
    nodes = list(graph.keys())
    matrix = [[0] * len(nodes) for _ in range(len(nodes))]
    for i, node in enumerate(nodes):
        distances = dijkstra(graph, node)
        for j, other_node in enumerate(nodes):
            matrix[i][j] = distances[other_node]
    return matrix

# 示例图
graph = {
    'A': {'B': 1, 'C': 4},
    'B': {'A': 1, 'C': 2, 'D': 5},
    'C': {'A': 4, 'B': 2, 'D': 1},
    'D': {'B': 5, 'C': 1}
}

# 计算距离矩阵
print(distance_matrix(graph))