Implementation of binary search to find the index of a char (if present) in a string. Linked PR #780

[VarunVishwakarma117]

Adding new code

Implementation of binary search to find the index of a char (if present) in a string is added.

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Pitch

I have checked the folder and this code is not implemented yet. I'm linking the PR to this issue. Please, assign it to me and do the rightful.
PR #780