车运动时和静止时被鸟拉屎的概率

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road_length = 100 ## 路的长度
shit_rate = 0.3 ## 鸟拉屎的概率
shit_pos = [p for p in range(0, road_length)] ## 路上可能出现鸟屎的位置, 假设等概率
car_length = 4 ## 车的长度
car_speed = 1 ## 车的速度
car_start = 0 ## 运动的车开始的位置
static_car = 0 ## 对照组, 静止的车的位置
sim_times = 100000000 ## 模拟时长
static_count = 0 ## 对照组, 静止的车被鸟拉屎的次数
move_count = 0 ## 运动的车被鸟拉屎的次数

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## 生成一个鸟拉屎的位置, 如果这个时间点没有鸟拉屎, 则输出-1(假设拉在了别的地方)
import random
def generate_shit(shit_rate, shit_pos):
    should_shit = random.random() < shit_rate
    shit_position = -1 if not should_shit else shit_pos[random.randrange(len(shit_pos))]
    return shit_position

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## 车的运动函数, 如果车运动到了路的末尾, 则又从末尾向头运动, 假设匀速
direction = car_speed
def move_car(car_start, car_length, road_length):
    global direction
    if (car_start + car_length) >= road_length:
        direction = -car_speed
    if car_start <= 0:
        direction = car_speed
    car_start = car_start + direction
    return car_start

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## 判断鸟屎是否拉在了车上
def hashit_car(car_start, car_length, shit_position):
    hashit = 1 if (car_start <= shit_position and shit_position < (car_start + car_length)) else 0
    return hashit

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for _ in range(sim_times):
    shit_position = generate_shit(shit_rate, shit_pos)
    car_start = move_car(car_start, car_length, road_length)

    has_static_shit = hashit_car(static_car, car_length, shit_position)
    has_move_shit = hashit_car(car_start, car_length, shit_position)

    static_count = static_count + has_static_shit
    move_count = move_count + has_move_shit

#     print(shit_position, static_car, has_static_shit, static_count, car_start, has_move_shit, move_count)

print(static_count, move_count, sim_times)
print(static_count / sim_times, move_count / sim_times)