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  • 用 Python 解答两道来自阿里伯乐系统的笔试题

    目录

    前言

    朋友到阿里面试,分享两道小题,博主比较闲就试着用 Python 解答一下,实现方式肯定是多种多样的,优劣也会各有不同,欢迎交流。

    题目一

    三个线程交替打印 abcabcabc…,一个打印 a,一个打印 b,一个打印 c。

    分析

    典型的线程同步问题,解决思路是互斥锁,三个线程通过锁来完成互斥下的协作同步。

    这里写图片描述

    实现

    import threading
    
    
    lock_a = threading.Lock()
    lock_b = threading.Lock()
    lock_c = threading.Lock()
    
    
    def print_a(num):
        if num < 0:
            return
    
        lock_a.acquire()
        print('a')
        lock_b.release()
    
        print_a(num-1)
    
    
    def print_b(num):
        if num < 0:
            return
    
        lock_b.acquire()
        print('b')
        lock_c.release()
    
        print_b(num-1)
    
    
    def print_c(num):
        if num < 0:
            return
    
        lock_c.acquire()
        print('c')
        lock_a.release()
    
        print_c(num-1)
    
    
    def main():
        num = 9
    
        thread_a = threading.Thread(target=print_a, args=(num,))
        thread_b = threading.Thread(target=print_b, args=(num,))
        thread_c = threading.Thread(target=print_c, args=(num,))
    
        lock_b.acquire()
        lock_c.acquire()
        thread_a.start()
        thread_b.start()
        thread_c.start()
    
    
    if __name__ == '__main__':
        main()

    题目二

    有一个 String 类型数组 arr = { "a", "b", "d", "d", "a", "d", "a", "e", "d", "c" },请编码实现统计该数组中字符重复次数并由多到少的顺序对 a,b,c,d,e 重新排序输出。

    分析

    如果用 C 语言实现,那么姑且还是一道冒泡排序算法题。对于 Python 而言,这题就是比较单纯的熟练度考验,使用 collections 模块可以轻松实现。

    实现

    from collections import Counter
    
    
    li1 = ["a", "b", "d", "d", "a", "d", "a", "e", "d", "c"]
    print(Counter(li1))

    from collections import defaultdict
    from collections import OrderedDict
    
    
    li1 = ["a", "b", "d", "d", "a", "d", "a", "e", "d", "c"]
    d = defaultdict(int)
    
    
    for k in li1:
        d[k] += 1
    print OrderedDict(sorted(d.items(), key=lambda t: t[1], reverse=True))
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  • 原文地址:https://www.cnblogs.com/hzcya1995/p/13310534.html
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