Less time complexity for gcd.cpp and oddEven.cpp

[abhishekkujur1307]

Description

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Program Name - #197 #265 Issue No.-

Type issue number after hash(#)

Checklist(self check)

• [x] Yes, this task assigned to me.
• [x] My code follows the style guidelines(Clean Code) of this project
• [x] I have performed a self-review of my own code
• [x] My Filename is in camelCase format
• [x] I have added Problem statement, Problem link in file.

[aayushi-droid]

wrong issue numbers