feat: Update free-courses-en.md - adding resource for C++ interview prep (#10851)

* Update free-courses-en.md - adding resource for C++ interview prep

* fix: lint errors

* feat: updated problem-sets-competitive-programming list.md

* fix: linter errors

* fix: linter errors

* fix: title name

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Co-authored-by: abhargava3 <ayushi_bhargava@intuit.com>

more/problem-sets-competitive-programming.md

@@ -98,6 +98,7 @@
 
 ### Problem Sets
 
+* [#C++](https://www.youtube.com/playlist?list=PLliXPok7ZonkJEe0cUbVZ3umyKbFA-Dd9) - Keerti Purswani
 * [100 Days CSS Challenge](https://100dayscss.com) - Matthias Martin *(Codepen account requested, not required)*
 * [500 Data structures and algorithms interview questions and their solutions in C++](https://www.quora.com/q/techiedelight/500-Data-Structures-and-Algorithms-interview-questions-and-their-solutions)
 * [Abekus | Free Practice Questions with Solutions](https://abekus.com)