Python实现简单查找最长子串功能示例


						本文实例讲述了Python实现简单查找最长子串功能。分享给大家供大家参考，具体如下：

题目选自edX公开课 MITx: 6.00.1x Introduction to Computer Science and Programming 课程 Week2 的Problem Set 1的第三题。下面是原题内容。



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, ifs = '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

For problems such as these, do not include raw_input statements or define the variable s in any way. Our automated testing will provide a value of s for you - so the code you submit in the following box should assume s is already defined. If you are confused by this instruction, please review L4 Problems 10 and 11 before you begin this problem set.



代码如下：





# -*- coding:utf-8 -*-

#! python2

#判断一个字符串内的字母是否是按字母表顺序

# 如IsStrIncre('abbcdg') 返回 True

# IsStrIncre('abbadg') 返回 False

# 如果只有一个字符，也返回False

def IsStrIncre(s):

  for cnt in range(len(s) - 1):

    if len(s) == 1:

      return False

    elif s[cnt] > s[cnt+1]:

      return False

  return True

s = 'abajsiesnwdw'# example code

substr = ''

for length in range(1, len(s)+1):

  firstflag = True # a flag to remember the first string that satisfied the requirements

           # and ignore the strings satisfied the requirements but appeared after

  for cnt in range(len(s)-length+1):

    if IsStrIncre(s[cnt: cnt+length]):

      if firstflag:

        substr = s[cnt: cnt+length]

        firstflag = False

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







运行结果：



Longest substring in alphabetical order is: ajs



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希望本文所述对大家Python程序设计有所帮助。