Python 单词计数器

Question

我在学校上 Python 2.7 课程，他们告诉我们创建以下程序：

Assume s is a string of lower case characters.

Write a program that prints the longest substring of s in which the letters occur in alphabetical order.

For example, if s = azcbobobegghakl , then your program should print

Longest substring in alphabetical order is: beggh

In the case of ties, print the first substring.

For example, if s = 'abcbcd', then your program should print

Longest substring in alphabetical order is: abc

我写了下面的代码：

s = 'czqriqfsqteavw'

string = ''

tempIndex = 0
prev = ''
curr = ''

index = 0
while index < len(s):
    curr = s[index]
    if index != 0:
        if curr < prev:
            if len(s[tempIndex:index]) > len(string):
               string = s[tempIndex:index]
            tempIndex=index
        elif index == len(s)-1:
            if len(s[tempIndex:index]) > len(string):
               string = s[tempIndex:index+1]
    prev = curr
    index += 1

print 'Longest substring in alphabetical order is: ' + string

老师还给了我们一系列的测试字符串来试一下：

onyixlsttpmylw  
pdxukpsimdj  
yamcrzwwgquqqrpdxmgltap  
dkaimdoviquyazmojtex  
abcdefghijklmnopqrstuvwxyz  
evyeorezmslyn  
msbprjtwwnb  
laymsbkrprvyuaieitpwpurp  
munifxzwieqbhaymkeol   
lzasroxnpjqhmpr    
evjeewybqpc   
vzpdfwbbwxpxsdpfak    
zyxwvutsrqponmlkjihgfedcba  
vzpdfwbbwxpxsdpfak     
jlgpiprth  
czqriqfsqteavw

除了最后一个，它们都工作正常，它产生以下答案：

Longest substring in alphabetical order is: cz

但它应该说：

Longest substring in alphabetical order is: avw

代码我已经检查了一千遍了，没有发现错误。你能帮帮我吗？

Answer 1

这些行：

        if len(s[tempIndex:index]) > len(string):
           string = s[tempIndex:index+1]

不同意对方。如果新的最佳字符串是 s[tempIndex:index+1] 那么这就是您应该在 if 条件中比较其长度的字符串。将它们更改为彼此一致可以解决问题：

        if len(s[tempIndex:index+1]) > len(string):
           string = s[tempIndex:index+1]

Answer 2

我看到 user5402 很好地回答了您的问题，但这个特殊问题引起了我的兴趣，所以我决定重写您的代码。 :) 下面的程序使用与您的代码基本相同的逻辑，只是做了一些小改动。

在可行时避免使用索引并直接遍历字符串（或其他容器对象）的内容被认为更符合 Pythonic。这通常会使代码更易于阅读，因为我们不必同时跟踪索引和内容。

为了访问字符串中的当前字符和前一个字符，我们将输入字符串的两个副本压缩在一起，其中一个副本通过在开头插入 space 字符进行偏移。我们还在另一个副本的末尾附加了一个 space 字符，这样当最长有序子序列出现在输入字符串的末尾时，我们就不必进行特殊处理。

#! /usr/bin/env python

''' Find longest ordered substring of a given string 

    From 
    Written by PM 2Ring 2015.01.14
'''

data = [
    "azcbobobegghakl",
    "abcbcd",
    "onyixlsttpmylw",
    "pdxukpsimdj",
    "yamcrzwwgquqqrpdxmgltap",
    "dkaimdoviquyazmojtex",
    "abcdefghijklmnopqrstuvwxyz",
    "evyeorezmslyn",
    "msbprjtwwnb",
    "laymsbkrprvyuaieitpwpurp",
    "munifxzwieqbhaymkeol",
    "lzasroxnpjqhmpr",
    "evjeewybqpc",
    "vzpdfwbbwxpxsdpfak",
    "zyxwvutsrqponmlkjihgfedcba",
    "vzpdfwbbwxpxsdpfak",
    "jlgpiprth",
    "czqriqfsqteavw",
]


def longest(s):
    ''' Return longest ordered substring of s
        s consists of lower case letters only.
    '''
    found, temp = [], []
    for prev, curr in zip(' ' + s, s + ' '):
        if curr < prev:
            if len(temp) > len(found):
                found = temp[:]
            temp = []
        temp += [curr]
    return ''.join(found)


def main():
    msg = 'Longest substring in alphabetical order is:'
    for s in data:
        print s
        print msg, longest(s)
        print


if __name__ == '__main__':
    main()

输出

azcbobobegghakl
Longest substring in alphabetical order is: beggh

abcbcd
Longest substring in alphabetical order is: abc

onyixlsttpmylw
Longest substring in alphabetical order is: lstt

pdxukpsimdj
Longest substring in alphabetical order is: kps

yamcrzwwgquqqrpdxmgltap
Longest substring in alphabetical order is: crz

dkaimdoviquyazmojtex
Longest substring in alphabetical order is: iquy

abcdefghijklmnopqrstuvwxyz
Longest substring in alphabetical order is: abcdefghijklmnopqrstuvwxyz

evyeorezmslyn
Longest substring in alphabetical order is: evy

msbprjtwwnb
Longest substring in alphabetical order is: jtww

laymsbkrprvyuaieitpwpurp
Longest substring in alphabetical order is: prvy

munifxzwieqbhaymkeol
Longest substring in alphabetical order is: fxz

lzasroxnpjqhmpr
Longest substring in alphabetical order is: hmpr

evjeewybqpc
Longest substring in alphabetical order is: eewy

vzpdfwbbwxpxsdpfak
Longest substring in alphabetical order is: bbwx

zyxwvutsrqponmlkjihgfedcba
Longest substring in alphabetical order is: z

vzpdfwbbwxpxsdpfak
Longest substring in alphabetical order is: bbwx

jlgpiprth
Longest substring in alphabetical order is: iprt

czqriqfsqteavw
Longest substring in alphabetical order is: avw

Answer 3

指数是你的朋友。下面是问题的简单代码。

longword = ''

for x in range(len(s)-1):
    for y in range(len(s)+1):
        word = s[x:y]
        if word == ''.join(sorted(word)):
            if len(word) > len(longword):
                longword = word
print ('Longest substring in alphabetical order is: '+ longword)

Answer 4

我自己也遇到过这个问题，我想我会分享我的答案。

我的解决方案 100% 有效。

问题是帮助 Python 编码新手理解循环，而不必深入研究其他复杂的解决方案。这段代码更扁平，并使用变量名，便于新编码人员阅读。

我添加了注释来解释代码步骤。没有评论它非常干净和可读。

s = 'czqriqfsqteavw'

test_char = s[0]
temp_str = str('')
longest_str = str('')

for character in s:

    if temp_str == "":                   # if empty = we are working with a new string
        temp_str += character            # assign first char to temp_str
        longest_str = test_char          # it will be the longest_str for now

    elif character >= test_char[-1]:     # compare each char to the previously stored test_char
        temp_str += character            # add char to temp_str
        test_char = character            # change the test_char to the 'for' looping char

        if len(temp_str) > len(longest_str): # test if temp_char stores the longest found string
            longest_str = temp_str           # if yes, assign to longest_str

    else:
        test_char = character            # DONT SWAP THESE TWO LINES.
        temp_str = test_char             # OR IT WILL NOT WORK.

print("Longest substring in alphabetical order is: {}".format(longest_str))

Answer 5

我的解决方案与 Nim J 的解决方案类似，但迭代次数较少。

res = ""

for n in range(len(s)):
     for i in range(1, len(s)-n+1):
        if list(s[n:n+i]) == sorted(s[n:n+i]):
            if len(list(s[n:n+i])) > len(res):
                res = s[n:n+i]

print("Longest substring in alphabetical order is:", res)

Python 单词计数器

Python word counter

python

string

python-2.7