Question

所以，我刚刚开始关注coursera.org的新算法课程。由于课程是在JAVA中，我不想同时学习Java +算法，我将JAVA样本“翻译”为python。但是，我有点卡住，因为应该更快的算法表现更差。对我而言，奇怪的是，当我运行测试时输入量很大，速度较慢的算法是最快的... ...我认为这与我实例化的数组（ids）发生的奇怪事情有关。不同的对象：

import time
from utils.benchmark import *
from quickunion import *
from quickunion_weighted import *
from quickfind import *

# create only one array of id's so the comparison is fair
ids = random_tree(10)

my_trees = [QuickFindUF, QuickUnionUF, 
        QuickUnionWeighted, QuickUnionPathCompression]

print "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n"

def test(classes, tree):
    for e in classes:
        tmp = e(arr=tree)
        print tmp.id
        print "%s:" % tmp.__class__.__name__
        t = time.clock()
        print "\tare 3 and 6 connected?: %s" % tmp.connected(3, 6)
        "\tunion(3, 6): "
        tmp.union(3,6)
        print "\tare 3 and 6 connected?: %s" % tmp.connected(3, 6)
        print "Total time: {0} ".format(time.clock()-t)

if __name__ == '__main__':
    test(my_trees, ids)

这将打印以下结果：

[1, 8, 1, 7, 4, 8, 5, 7, 8, 2]
QuickFindUF:
    are 3 and 6 connected?: False
    are 3 and 6 connected?: True
Total time: 2.7e-05 
[1, 8, 1, 5, 4, 8, 5, 5, 8, 2]
QuickUnionUF:
    are 3 and 6 connected?: True
    are 3 and 6 connected?: True
Total time: 2.6e-05 
[1, 8, 1, 5, 4, 8, 5, 5, 8, 2]
QuickUnionWeighted:
    are 3 and 6 connected?: True
    are 3 and 6 connected?: True
Total time: 2.8e-05 
[1, 8, 1, 5, 4, 8, 5, 5, 8, 2]
QuickUnionPathCompression:
    are 3 and 6 connected?: True
    are 3 and 6 connected?: True
Total time: 2.7e-05

出于某种原因，除了QuickFindUF实例之外，在比较之前数组都会被更改。有什么想法吗？

这是我创建的回购：https://github.com/herrmendez/python-algorithms

Answer 1

您的算法正在修改传入的列表实例.Python没有通过可复制值获取参数的概念;每个绑定名称都是按值传递的对象引用，但某些对象类型是不可变的。

将算法传递给列表的副本：

from copy import deepcopy

...

    tmp = e(arr=deepcopy(tree))

Python：将数组传递给对象时的奇怪行为

1 个答案: