Longest substring in a string

Python
1

Hello,

I have the following assignment:

’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ‘’ ’ ’ ‘’ ’ ’ ’

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
’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ’ ‘’ ’ ’ ‘’ ’ ’ ’

I have no idea on the outline of this algoroithm. Could somoeone please give me an idea?

Thank you.

2

english letters all have ASCII values. The ascii values are all contiguous in the lower case set of letters. (from 97 to 122)
If you can find a way to transform the letters to a list of ascii values then you can easily see sequences in the numbers.

Eg. if you had 97 98 99 (for a b c ) followed by 98 99 (b c)
then you can see that 97,98,99 is the longest sequence and translate that back to abc

3

Thanks a lot. I’ll try it.

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