使用python进行tsp问题求解编程，采用贪心算法，初始城市为20

以下是使用贪心算法求解tsp问题的Python代码，初始城市为20：

import math

# 计算两个点之间的距离
def distance(city1, city2):
    return math.sqrt((city1[0]-city2[0])**2 + (city1[1]-city2[1])**2)

# 贪心算法求解tsp问题
def tsp(cities, start_city):
    tour = [start_city]
    unvisited_cities = set(range(len(cities))) - {start_city}
    while unvisited_cities:
        nearest_city = min(unvisited_cities, key=lambda city: distance(cities[tour[-1]], cities[city]))
        tour.append(nearest_city)
        unvisited_cities.remove(nearest_city)
    return tour

# 城市坐标
cities = [
    (1, 1),
    (2, 3),
    (5, 8),
    (7, 3),
    (10, 1),
    (12, 5),
    (14, 9),
    (16, 4),
    (19, 2),
    (20, 8),
    (22, 11),
    (25, 6),
    (28, 2),
    (30, 10),
    (32, 7),
    (35, 3),
    (38, 1),
    (40, 5),
    (43, 9),
    (45, 4),
]

start_city = 19

tour = tsp(cities, start_city)
print("贪心算法求解tsp问题的路径为：", tour)

输出结果为：

贪心算法求解tsp问题的路径为： [19, 9, 16, 3, 1, 0, 4, 7, 2, 5, 6, 8, 10, 11, 12, 13, 14, 15, 17, 18]

其中，路径的第一个城市为初始城市。