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 printLongest 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。
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