Algorithm to find substring within a string or a paragraph

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Finding substring

Often we come across interview questions like , find all occurances of a given substring within a string.
What are the best possible strategies to solve this problem ? Well, there could be many but today in this blog
I will consider explaining the simplest and most straightforawrd way of looking for a substring within a given
string and it’s linear search (costly though, but this algorithm can be optimized).

Below is a small C program that explains the solution to the above problem:

ID provided is not a Gistpen repo.

Below is the link to compile and execute the above code:
Substring pattern match
Let’s try to understand what the above program does:

It has a nested loop. The outer loop loops through the given string parsing the string character by character.
The inner loop parses the substring character by character and looking for a possible match of it’s first character
to that of the current character of the main string. If the characters match, it does a stnrcmp() wherein it will
compare N characters (N = length of substring) starting from current index and if a match is encountered, the index is
pushed into the array. This iteration goes till the length of the main string.
This algorithm can be further extended to create a find and replace functionality which will be the topic of my next
blog. Stay tuned for more interesting stuff and please comment if there are any doubts in this one.




An avid reader, responsible for generating creative content ideas for His interests include algorithms and programming languages. Blogging is a hobby and passion.

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