1 
P1  Divisiblity of Differences 
Codeforces 
Codeforces Round #441 (Div. 2, by Moscow Team Olympiad) 
2 
P2  Recursive Queries 
Codeforces 
ICM Technex 2018 and Codeforces Round #463 (Div. 1 + Div. 2, combined) 
3 
P3  Countries at War 
URI 

4 
P4  Probability One 
SPOJ 

5 
P5  Devlali Numbers 
SPOJ 

6 
P6  Sequence of Sequence 
URI 

7 
P7  Vladik and fractions 
Codeforces 
Codeforces Round #384 (Div. 2) 
8 
P8  Appleman and Card Game 
Codeforces 
Codeforces Round #263 (Div. 2) 
9 
P9  Binary String Constructing 
Codeforces 
Codeforces Round #494 (Div. 3) 
10 
P10  New Year Permutation 
Codeforces 
Good Bye 2014 
11 
P11  Adding Digits 
Codeforces 
Codeforces Round #158 (Div. 2) 
12 
P12  Tea Queue 
Codeforces 
Educational Codeforces Round 37 (Rated for Div. 2) 
13 
P13  The Time 
Codeforces 
Educational Codeforces Round 7 
14 
P14  Many Equal Substrings 
Codeforces 
Codeforces Round #506 (Div. 3) 
15 
P15  Beautiful Divisors 
Codeforces 
Educational Codeforces Round 33 (Rated for Div. 2) 
16 
P16  Big Segment 
Codeforces 
Codeforces Round #149 (Div. 2) 
17 
P17  Eevee 
Codeforces 
MemSQL Start[c]UP 2.0  Round 1 
18 
P18  Little Pony and Expected Maximum 
Codeforces 
Codeforces Round #259 (Div. 1) & Codeforces Round #259 (Div. 2) 
19 
P19  DZY Loves Sequences 
Codeforces 
Codeforces Round #255 (Div. 1) & Codeforces Round #255 (Div. 2) 
20 
P20  Pasha and Tea 
Codeforces 
Codeforces Round #311 (Div. 2) 
21 
P21  Vasya and Book 
Codeforces 
Educational Codeforces Round 55 (Rated for Div. 2) 
22 
P22  Xenia and Divisors 
Codeforces 
Codeforces Round #199 (Div. 2) 
23 
P23  Mister B and Book Reading 
Codeforces 
Codeforces Round #421 (Div. 2) 
24 
P24  Bicycle Chain 
Codeforces 
Codeforces Round #132 (Div. 2) 
25 
P25  Mahmoud and Ehab and the bipartiteness 
Codeforces 
Codeforces Round #435 (Div. 2) 
26 
P26  Bear and Friendship Condition 
Codeforces 
VK Cup 2017  Round 1 
27 
P27  Table Tennis 
Codeforces 
Codeforces Round #443 (Div. 2) 
28 
P28  MUH and Important Things 
Codeforces 
Codeforces Round #269 (Div. 2) 
29 
P29  Second Order Statistics 
Codeforces 
Codeforces Beta Round #22 (Div. 2 Only) 
30 
P30  Taxes 
Codeforces 
Codeforces Round #382 (Div. 2) & Codeforces Round #382 (Div. 1) 
31 
P31  Okabe and Future Gadget Laboratory 
Codeforces 
Codeforces Round #420 (Div. 2) 
32 
P32  Vasya and Golden Ticket 
Codeforces 
Technocup 2019  Elimination Round 1 
33 
P33  Alphabetic Removals 
Codeforces 
Codeforces Round #490 (Div. 3) 
34 
P34  New Year and Buggy Bot 
Codeforces 
Good Bye 2017 
35 
P35  Cyclic Components 
Codeforces 
Codeforces Round #479 (Div. 3) 
36 
P36  Bits 
Codeforces 
Codeforces Round #276 (Div. 1) & Codeforces Round #276 (Div. 2) 
37 
P37  Design Tutorial: Make It Nondeterministic 
Codeforces 
Codeforces Round #270 
38 
P38  Dima and Todo List 
Codeforces 
Codeforces Round #214 (Div. 2) 
39 
P39  Consecutive Subsequence 
Codeforces 
Codeforces Round #479 (Div. 3) 
40 
P40  Tiling with Hexagons 
Codeforces 
Codeforces Round #133 (Div. 2) 
41 
P41  Nuts 
Codeforces 
Codeforces Round #236 (Div. 2) 
42 
P42  Sereja and Contests 
Codeforces 
Codeforces Round #235 (Div. 2) 
43 
P43  Unbearable Controversy of Being 
Codeforces 
Codeforces Round #277.5 (Div. 2) 
44 
P44  Kuro and Walking Route 
Codeforces 
Codeforces Round #482 (Div. 2) 
45 
P45  Zebras 
Codeforces 
Codeforces Round #469 (Div. 1) & Codeforces Round #469 (Div. 2) 
46 
P46  Vasya and Arrays 
Codeforces 
Educational Codeforces Round 50 (Rated for Div. 2) 
47 
P47  Arpa and an exam about geometry 
Codeforces 
Codeforces Round #432 (Div. 2, based on IndiaHacks Final Round 2017) 
48 
P48  Little Xor 
Codeforces 
Codeforces Round #153 (Div. 2) 
49 
P49  Hongcow Solves A Puzzle 
Codeforces 
Codeforces Round #385 (Div. 2) 
50 
P50  kFactorization 
Codeforces 
Educational Codeforces Round 19 
51 
P51  Permutation Cycle 
Codeforces 
ICM Technex 2018 and Codeforces Round #463 (Div. 1 + Div. 2, combined) 
52 
P52  Help Far Away Kingdom 
Codeforces 
Codeforces Beta Round #78 (Div. 2 Only) 
53 
P53  Postcards and photos 
Codeforces 
Codeforces Beta Round #98 (Div. 2) 
54 
P54  Reconnaissance 
Codeforces 
Codeforces Beta Round #32 (Div. 2, Codeforces format) 
55 
P55  Ladder 
Codeforces 
Codeforces Round #171 (Div. 2) 
56 
P56  Spotlights 
Codeforces 
Technocup 2017  Elimination Round 2 
57 
P57  Lakes in Berland 
Codeforces 
Codeforces Round #375 (Div. 2) 
58 
P58  Mysterious Present 
Codeforces 
Codeforces Beta Round #4 (Div. 2 Only) 
59 
P59  Diplomas and Certificates 
Codeforces 
Educational Codeforces Round 24 
60 
P60  Wet Shark and Flowers 
Codeforces 
Codeforces Round #341 (Div. 2) 
61 
P61  The Contest 
Codeforces 
Educational Codeforces Round 22 
62 
P62  Network Topology 
Codeforces 
Croc Champ 2013  Round 1 
63 
P63  Dasha and Password 
Codeforces 
Codeforces Round #394 (Div. 2) 
64 
P64  Card Game 
Codeforces 
Codeforces Beta Round #82 (Div. 2) 
65 
P65  Bear and Colors 
Codeforces 
VK Cup 2016  Round 3 
66 
P66  Sereja and Array 
Codeforces 
Codeforces Round #187 (Div. 2) 
67 
P67  Mystical Mosaic 
Codeforces 
VK Cup 2018  Round 2 
68 
P68  I Wanna Be the Guy 
Codeforces 
Codeforces Round #268 (Div. 2) 
69 
P69  Pizza, Pizza, Pizza!!! 
Codeforces 
Codeforces Round #482 (Div. 2) 
70 
P70  I'm bored with life 
Codeforces 
Codeforces Round #422 (Div. 2) 
71 
P71  Amusing Joke 
Codeforces 
Codeforces Round #101 (Div. 2) 
72 
P72  Greed 
Codeforces 
Codeforces Round #446 (Div. 2) 
73 
P73  Polycarp's Practice 
Codeforces 
Codeforces Round #498 (Div. 3) 
74 
P74  Dima and Friends 
Codeforces 
Codeforces Round #167 (Div. 2) 
75 
P75  Anton and Classes 
Codeforces 
Codeforces Round #404 (Div. 2) 
76 
P76  Present from Lena 
Codeforces 
Codeforces Beta Round #89 (Div. 2) 
77 
P77  Twins 
Codeforces 
Codeforces Round #111 (Div. 2) 
78 
P78  Helpful Maths 
Codeforces 
Codeforces Round #197 (Div. 2) 
79 
P79  Queue 
Codeforces 
Codeforces Round #303 (Div. 2) 
80 
P80  Sereja and Suffixes 
Codeforces 
Codeforces Round #215 (Div. 2) 