Wavelet Trees for competitive programming | IOI preparation #3

A short lecture on wavelet trees data structure, version for competitive programming, something different than standard memory-efficient bit-trick wavelet trees. Article link: https://users.dcc.uchile.cl/~jperez/p... Three problems on SPOJ: Wavelet tree problems on SPOJ: https://www.spoj.com/problems/ILKQUERY/ https://www.spoj.com/problems/ILKQUERY2/ https://www.spoj.com/problems/ILKQUERY3/ Frequently Asked Questions: https://github.com/Errichto/youtube/w... Github repository: https://github.com/Errichto/youtube Facebook:   / errichto   Twitter:   / errichto   Competitive Programming Discord: https://discordapp.com/invite/UzaURu7 Youtube channel 1:    / errichto   (mainly short videos) Youtube channel 2:    / errichto2   (streams) I’m Kamil Dębowski, better known as Errichto. I compete in and organize programming competitions. I make educational streams on Youtube and Twitch. I'm a finalist of ACM-ICPC, Topcoder Open, Facebook Hacker Cup and Google Code Jam. I got a second place in Google Code Jam 2018. I am/was nutella in Codeforces and target in Topcoder. Watch me if you want to practice for coding interviews, competitive programming or just algorithms in general. I share my thought process, explain everything, and mention similar problems and techniques/algorithms.