05 算法之狄克斯特拉-python实现

狄克斯特拉算法，找出图中权重最小的路径

#!python
#coding=utf-8

"""
狄克特斯拉算法
有以下图：
start --6-->a
start --2-->b
a     --1-->end
b     --5-->end
b     --3-->a
使用迪克斯特拉算法找出start-->end
权重最小的路径
"""
def build_graph():
    graph = {}
    graph["start"] = {"a": 6, "b": 2}
    graph["a"] = {"end": 1}
    graph["b"] = {"end": 5, "a": 3}
    graph["end"] = {}
    return graph

def dijkstra():
    graph = build_graph()
    # 无穷大
    infinity = float("inf")
    costs = {"a": 6, "b": 2, "end": infinity}
    parents = {"a": "start", "b": "start", "end": None}
    # 已处理过的节点
    processed = []

    # 找出开销最低的节点名称
    node = find_lowest_cost(costs, processed)
    while node is not None:
        cost = costs[node]
        # 找出邻居节点
        neighbors = graph[node]
        for key in neighbors.keys():
            new_cost = cost + neighbors[key]
            if costs[key] > new_cost:
                costs[key] = new_cost
                parents[key] = node
        processed.append(node)
        node = find_lowest_cost(costs, processed)
    print(costs)
    print(parents)

"""
找到权重最低的节点
"""
def find_lowest_cost(costs, processed):
    # 最小权重，初始化设置成无穷大
    lowest_cost = float("inf")
    lowest_node = None
    for node in costs:
        cost = costs[node]
        if cost < lowest_cost and node not in processed:
            lowest_cost = cost
            lowest_node = node
    return lowest_node


dijkstra()