给出Yen’s algorithm的标准代码

Yen's algorithm是一种寻找k最短路径的有效方法，它通常基于Dijkstra算法的变体。以下是Yen's algorithm的基本步骤和一种简单的Python代码实现（这里假设我们使用了Python的`heapq`库来管理最小堆）：

import heapq

def yen_algorithm(graph, source, k):
    shortest_paths = {source: (0, [])}  # 初始化源点的路径长度和路径
    paths_queue = [(0, source)]  # 用堆存储路径长度及对应顶点

    while len(shortest_paths) < k and paths_queue:
        distance, current_node = heapq.heappop(paths_queue)

        for neighbor, weight in graph[current_node].items():
            if neighbor not in shortest_paths or distance + weight < shortest_paths[neighbor][0]:
                new_distance = distance + weight
                shortest_paths[neighbor] = (new_distance, [current_node] + shortest_paths[neighbor][1])
                heapq.heappush(paths_queue, (new_distance, neighbor))

    return shortest_paths.values()[:k]  # 返回k条最短路径

# 示例：给定一个图的邻接矩阵表示
graph = {
    'A': {'B': 1, 'C': 4},
    'B': {'A': 1, 'D': 5},
    'C': {'A': 4, 'D': 2},
    'D': {'B': 5, 'C': 2}
}

shortest_paths = yen_algorithm(graph, 'A', 3)

这个版本的Yen's算法会返回源点'A'出发的前k条最短路径。注意实际应用中，你需要提供更具体的图数据结构（例如邻接列表或边集）以及相应的权重函数。