1 
P1  Dependency Problems 
SPOJ 

2 
P2  Nop 
SPOJ 

3 
P3  Leaves 
SPOJ 

4 
P4  Glass Carving 
Codeforces 
Codeforces Round #296 (Div. 2) & Codeforces Round #296 (Div. 1) 
5 
P5  New Password 
Codeforces 
VK Cup 2017  Qualification 2 
6 
P6  Xenia and Weights 
Codeforces 
Codeforces Round #197 (Div. 2) 
7 
P7  Bubble Sort Graph 
Codeforces 
Codeforces Round #198 (Div. 2) & Codeforces Round #198 (Div. 1) 
8 
P8  Stripe 
Codeforces 
Codeforces Beta Round #18 (Div. 2 Only) 
9 
P9  Transformation: from A to B 
Codeforces 
Technocup 2017  Elimination Round 1 (Unofficially Open for Everyone, Rated for Div. 2) 
10 
P10  Ilya and tictactoe game 
Codeforces 
Codeforces Round #390 (Div. 2) 
11 
P11  Binary Protocol 
Codeforces 
Educational Codeforces Round 25 
12 
P12  Pythagorean Triples 
Codeforces 
Codeforces Round #368 (Div. 2) 
13 
P13  Restaurant Tables 
Codeforces 
Codeforces Round #423 (Div. 2, rated, based on VK Cup Finals) 
14 
P14  Simple Minded Hashing 
UVA 

15 
P15  Box 
UVA 

16 
P16  Bender Problem 
Codeforces 
Codeforces Beta Round #28 (Codeforces format) 
17 
P17  Greg and Friends 
Codeforces 
Codeforces Round #179 (Div. 1) & Codeforces Round #179 (Div. 2) 
18 
P18  Magical Boxes 
Codeforces 
Codeforces Round #165 (Div. 1) & Codeforces Round #165 (Div. 2) 
19 
P19  Road Problem 
Codeforces 
School Team Contest #3 (Winter Computer School 2010/11) 
20 
P20  Martian Luck 
Codeforces 
Codeforces Round #133 (Div. 2) 