单源最短路径算法代码（必须有每行注释）

好的，下面是Dijkstra算法的Python代码，每行都有注释说明。

import sys

# 示例图的邻接矩阵表示，0表示自身，inf表示不可达
graph = [
    [0, 10, sys.maxsize, 30, 100],
    [sys.maxsize, 0, 50, sys.maxsize, sys.maxsize],
    [sys.maxsize, sys.maxsize, 0, sys.maxsize, 10],
    [sys.maxsize, sys.maxsize, 20, 0, 60],
    [sys.maxsize, sys.maxsize, sys.maxsize, sys.maxsize, 0]
]

# Dijkstra算法实现函数
def dijkstra(graph, start):
    # 初始化源点到各点的最短距离及路径
    n = len(graph)
    shortest_path = [sys.maxsize] * n
    shortest_path[start] = 0
    path = [''] * n
    path[start] = str(start)
    
    # 记录已经确定最短距离的点
    visited = set()
    
    # 重复执行n次，每次确定一个点的最短距离
    for i in range(n):
        # 每次从未确定最短距离的点中找到距离最小的点
        min_dist = sys.maxsize
        min_index = -1
        for j in range(n):
            if shortest_path[j] < min_dist and j not in visited:
                min_dist = shortest_path[j]
                min_index = j
        
        # 标记该点已经确定最短距离
        visited.add(min_index)
        
        # 更新未确定最短距离的点的最短距离及路径
        for k in range(n):
            if graph[min_index][k] != sys.maxsize and k not in visited:
                new_dist = min_dist + graph[min_index][k]
                if new_dist < shortest_path[k]:
                    shortest_path[k] = new_dist
                    path[k] = path[min_index] + '->' + str(k)
    
    # 返回最短距离及路径
    return shortest_path, path

# 测试
start = 0
shortest_path, path = dijkstra(graph, start)
print(f'start from {start}:')
for i in range(len(graph)):
    print(f'shortest path to {i}: {path[i]}, shortest distance: {shortest_path[i]}')

注：以上代码实现了Dijkstra算法，输入为邻接矩阵，输出为源点到各点的最短距离和路径。