写出Dijkstra算法的代码

Dijkstra算法是一种用于寻找图中两点之间最短路径的贪心算法，通常应用于有向无环图(DAG)或加权图。以下是Python版本的Dijkstra算法实现：

import heapq

def dijkstra(graph, start):
    # 初始化距离字典，所有节点的距离设为无穷大，起点距离设为0
    distances = {node: float('infinity') for node in graph}
    distances[start] = 0
    
    # 优先级队列，存储待访问节点及其当前距离
    queue = [(0, start)]
    
    while queue:
        # 获取距离最小的节点
        current_distance, current_node = heapq.heappop(queue)
        
        # 如果已经找到更小的路径，则跳过这个节点
        if current_distance > distances[current_node]:
            continue
        
        # 遍历当前节点的所有邻居
        for neighbor, weight in graph[current_node].items():
            distance = current_distance + weight
            
            # 更新邻接节点的距离
            if distance < distances[neighbor]:
                distances[neighbor] = distance
                # 把更新后的邻居加入队列
                heapq.heappush(queue, (distance, neighbor))
                
    return distances

# 示例图的数据结构（键为节点，值为字典，表示到其他节点的边及权重）
graph = {
    'A': {'B': 5, 'C': 1},
    'B': {'A': 5, 'D': 3},
    'C': {'A': 1, 'D': 4},
    'D': {'B': 3, 'C': 4, 'E': 2},
    'E': {'D': 2}
}

start_node = 'A'
shortest_distances = dijkstra(graph, start_node)