# Problem Definition

## Description

Implement strStr().

strstr - locate a substring ( needle ) in a string ( haystack ).
Try not to use standard library string functions for this question.

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

NOTE: Good clarification questions:

* What should be the return value if the needle is empty?
* What if both haystack and needle are empty?
* For the purpose of this problem, assume that the return value should be -1 in both cases.

## Notes