Given two strings haystack and needle, return the index of the first occurrence of needle within haystack. If needle does not exist as a substring of haystack, return $-1$.

Constraints:

• $1 \leq$ haystack.length, needle.length $\leq 10^4$

• haystack and needle consist of only lowercase English characters

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We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.