Question

I need to implement string.IndexOf functionality without using any c# string search related built in methods.

Could you suggest a simple algorithm for this. Search does not involve really large strings. you can assume the maximum lenghth of the string to be search as 1000 characters.

Answer 1

Since this sounds like homework, I’ll provide guidance instead of a solution. There is a great overview of string search algorithms on Wikipedia:

http://en.wikipedia.org/wiki/String_searching_algorithm

Try implementing the Naïve string search as a good introduction to the subject.

The simplest and least efficient way to see where one string occurs
inside another is to check each place it could be, one by one, to see
if it’s there. So first we see if there’s a copy of the needle in the
first character of the haystack; if not, we look to see if there’s a
copy of the needle starting at the second character of the haystack;
if not, we look starting at the third character, and so forth. In the
normal case, we only have to look at one or two characters for each
wrong position to see that it is a wrong position, so in the average
case, this takes O(n + m) steps, where n is the length of the haystack
and m is the length of the needle; but in the worst case, searching
for a string like “aaaab” in a string like “aaaaaaaaab”, it takes
O(nm) steps.