1 
P1  Vacations 
Codeforces 
Codeforces Round #363 (Div. 1) & Codeforces Round #363 (Div. 2) 
2 
P2  Hard problem 
Codeforces 
Codeforces Round #367 (Div. 2) 
3 
P3  Let's Go Rolling! 
Codeforces 
School Personal Contest #1 (Winter Computer School 2010/11)  Codeforces Beta Round #38 (ACMICPC Rules) 
4 
P4  They Are Everywhere 
Codeforces 
Codeforces Round #364 (Div. 2) 
5 
P5  Animals 
Codeforces 
Codeforces Beta Round #35 (Div. 2) 
6 
P6  Tetrahedron 
Codeforces 
Codeforces Round #113 (Div. 2) 
7 
P7  Journey 
Codeforces 
Codeforces Round #428 (Div. 2) 
8 
P8  Bytelandian gold coins 
SPOJ 

9 
P9  Ilya and Queries 
Codeforces 
Codeforces Round #186 (Div. 2) 
10 
P10  Segments Removal 
Codeforces 
Codeforces Round #452 (Div. 2) 
11 
P11  Caesar's Legions 
Codeforces 
Codeforces Beta Round #89 (Div. 2) 
12 
P12  Timofey and a tree 
Codeforces 
Codeforces Round #395 (Div. 1) & Codeforces Round #395 (Div. 2) 
13 
P13  Modulo Sum 
Codeforces 
Codeforces Round #319 (Div. 2) 
14 
P14  Barcode 
Codeforces 
Codeforces Round #139 (Div. 2) 
15 
P15  Woodcutters 
Codeforces 
Codeforces Round #303 (Div. 2) 
16 
P16  George and Job 
Codeforces 
Codeforces Round #267 (Div. 2) 
17 
P17  Shockers 
Codeforces 
Codeforces Round #454 (Div. 1, based on Technocup 2018 Elimination Round 4) & Codeforces Round #454 (Div. 2, based on Technocup 2018 Elimination Round 4) 
18 
P18  String Typing 
Codeforces 
Educational Codeforces Round 40 (Rated for Div. 2) 
19 
P19  Two TVs 
Codeforces 
Educational Codeforces Round 27 
20 
P20  String Transformation 
Codeforces 
Educational Codeforces Round 39 (Rated for Div. 2) 
21 
P21  Timetable 
Codeforces 
Educational Codeforces Round 39 (Rated for Div. 2) 
22 
P22  RedGreen Towers 
Codeforces 
Codeforces Round #273 (Div. 2) 
23 
P23  Writing Code 
Codeforces 
Codeforces Round #302 (Div. 1) & Codeforces Round #302 (Div. 2) 