Slides :
https://www.canva.com/design/DAG11Q6gvg4/C6HUSJPN-lvOwlZ9WlVo-Q/edit
codes :
https://www.spoj.com/problems/CSUMQ/en/
sol : https://ideone.com/SKpnC8
https://codeforces.com/contest/433/problem/B
sol 1-based : https://ideone.com/81Tfvn
sol 0-based : https://ideone.com/gAkKy9
https://www.spoj.com/problems/UPDATEIT/en/
sol https://ideone.com/RsEWv3
https://codeforces.com/contest/816/problem/B
sol : https://ideone.com/3MuWcH
https://cses.fi/problemset/task/1652
sol : https://cses.fi/paste/31d0ad996df12ca2e5aecb/
https://www.codechef.com/problems/FREQARRY
sol : https://ideone.com/uP2HdA
