:-)

1.  https://www.geeksforgeeks.org/numeric-header-in-c-stl-set-1-accumulate-and-partial_sum/ 2.  https://codeforces.com/contest/1197/problem/C Time complexity-O(n*k)

Using Upper_bound 1.  https://codeforces.com/problemset/problem/474/B 2.  https://codeforces.com/problemset/problem/706/B Contest Link 1.  https://vjudge.net/contest/311179#status/Nipun_Paul/-/1/

https://www.programiz.com/c-programming/library-function/ctype.h/isalpha Solution example -  https://vjudge.net/contest/307320#status/Nipun_Paul/I/0/