Analyzing programming contest grandmasters' styles and tools - Gennady Korotkevich (tourist) vs Andrew He (ecnerwala) (2023-03-24)

delyan · March 24, 2024, 8:44pm

This post is a commentary and analysis based on this video, which shows a competition between Gennady Korotkevich (tourist) and Andrew He (ecnerwala):

Watch the video here: https://www.youtube.com/watch?v=bBNIIg8REUU

Gena’s Code

ChatGPT 4 was used to recover the first 6 characters from Gena’s code snippet.
We see on the screen

So we know that "using " is missing in the first line of using namespace std; etc. (6 characters)
We also know that tourist tends to start his solutions with the following comment:

/**
 *    author:  tourist
 *    created: 16.03.2018 20:33:14       
**/
#include <bits/stdc++.h>
 
using namespace std;

Gena also has a template for his main function:

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  /* solution goes here */
  return 0;
}

So the code from the screenshot above is most likely this:

/**
 *    author:  tourist
 *    created: 10.05.2020 20:33:59       
**/
#include <bits/stdc++.h>

using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n;
    cin >> n;
    
    map<int, int> mp;
    long long ans = 0;
    
    for (int i = 0; i < n; i++) {
        int a;
        cin >> a;
        
        ans += mp[i - a];
        mp[i + a]++;
    }
    
    cout << ans << '\n';
    
    return 0;
}

Andrew’s code

#include <bits/stdc++.h>

int main() {
    using namespace std;
    ios_base::sync_with_stdio(false), cin.tie(nullptr);
    
    int N; cin >> N;
    vector<int> H(N);
    for (int i = 0; i < N; i++) {
        cin >> H[i];
    }

    int64_t ans = 0;
    map<int, int> mp;
    for (int i = 0; i < N; i++) {
        // H[i] + H[j] = i - j
        ans += mp[H[i] - i];
    }

    cout << ans << '\n';
    return 0;
}

Toolboxes (or Who Uses What to Compete)

What’s in Gena’s Toolbox

Lets find out what Gennady Korotkevich uses for programming competitions.
Here is what Gena uses and how he operates:

OS: Windows 10
browsers: Firefox, Chrome
no apparent version control (VCS) system
MinGW
C++ (GCC 9.2.1) (what atcoder.jp uses to evaluate)
IDE/Editor: Far Manager (version 3.0.4900 x64 (as of May 2020))
Gena does not have a shortcut for executing sol.exe with test input
- he’s a fast typist
- leverages FAR’s history
  
  image726×299 43.5 KB

Gena’s Setup:

has some automation to create the directories for the competition ahead of time:
compiles with: C:\MinGW\MinGW\bin\g++.exe -O2 -Wall -Wl,--stack=268435456 -Wextra -std=c++17 !.! -o !.exe
executes the solution with: sol.exe <in1
based on the May 2020 video above there is no automation to submit the code. Gena copy/pastes from Far Manager to the competition website:

image724×934 49.1 KB
→
image729×825 62.9 KB

What’s in Andrew He’s toolbox

OS: macOS
IDE/Editor: NVIM / NeoVIM
- NeoVIM Solarized Light Theme

Andrew uses automation download_prob.py to speed up the setup for the contest:

Andrew compiles with some iteration of:

g++ -std=c++17 -O2 -Wall -Wextra -pedantic -Wshadow -Wformat=2 \
  -Wfloat-equal -Wconversion -Wlogical-op -Wcast-qual -Wcast-align \
  -Wno-unused-result -Wno-sign-conversion \
  -D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC -D_FORTIFY_SOURCE=2 \
  F.cpp -o F

What are all these flags?

-std=c++17 sets the C++ standard to C++17.
-O2 enables compiler optimizations.
-Wall enables all the warnings about constructions that are easy to avoid.
-Wextra enables extra warnings not covered by -Wall.
-pedantic ensures that the code adheres strictly to the standard.
-Wshadow warns whenever a local variable shadows another variable.
-Wformat=2 adds extra checks for printf/scanf, etc.
-Wfloat-equal warns if floating-point values are compared for equality.
-Wconversion warns for implicit conversions that may alter a value.
-Wlogical-op warns about suspicious uses of logical operators.
-Wcast-qual warns when a cast removes an attribute like const or volatile.
-Wcast-align warns where pointer casts increase alignment requirements.
-Wno-unused-result disables warnings for unused results.
-Wno-sign-conversion turns off warnings related to sign conversions.
-D_GLIBCXX_DEBUG enables macros for the debug version of the standard library.
-D_GLIBCXX_DEBUG_PEDANTIC is an even more pedantic version of the above.
-D_FORTIFY_SOURCE=2 adds security checks to detect buffer overflows.
F.cpp is the input source file to compile.
-o F specifies the output file name for the compiled executable.

It is interesting that Andrew keeps his competition solutions in a Dropbox folder →

~/Dropbox/programming/AtCoder/ABC166/D

Andrew’s files are under git revision control →

It is unclear from the video whether Andrew uses automation to submit his code to the judge or will do it manually (copy/paste from terminal?).

Far Manager

Configure Far Manager

here is an excellent guide: How to compile, run and debug C/C++ programs using Far Manager? - Codeforces

Create file associations in Far Manager.

Menu (F9) → Commands (C) → File associations (A)
Create a new file association (Insert):
- mask: *.cc (or however you name your C++ files)
- execute command for Enter: C:\MinGW\bin\g++.exe -O2 -Wall -Wl,--stack=268435456 -Wextra -std=c++17 !.! -o !.exe
- execute command for Ctrl+PgDn: C:\MinGW\bin\g++.exe -O2 -Wall -Wl,--stack=268435456 -Wextra -std=c++17 !.! -o !.exe -DDEBUG -g

Press Enter on your sol.cc file to execute command g++ -O2 -Wall -Wl,--stack=268435456 -Wextra -std=c++17 sol.cpp -o sol.exe. This will compile the C++ code from sol.cc to an executable sol.exe. This assumes that you have C:\MinGW\bin\g++.exe. (Get MinGW from Nuwen.net)

Alternatively you can record the keystrokes necessary to do this operation and bind them to a hotkey (such as F9). Here are the instructions.

Far Manager Shortcuts

Ctrl-A - file attributes (equivalen* t to F9, F, A)
Alt-F9 - maximize window
Alt-Shift-F9 - configure plugins
Ctrl-Alt-Shift - hide windows while the keys are held
F4 on a folder - edit folders attributes (ctrl-a)
alt-left, right, home, end - scroll long names
ctrl-ins - copy names of the selected files into clipboard (command line empty, ctrl-shift-ins if not empty)
ctrl-alt-ins - copy network (unc) names into clipboard
alt-shift-ins - copy full (with path) names into clipboard
ctrl-f - full file name from the actve panel, crtl-: from passive (equiv to crtl-], ctrl-enter)
ctrl-end - command string completion from the history (press again to go to the next matching history line)
alt-f8 - command history
alt-f10 - find folder
alt-f11 - view and edit history
alt-f12 - folder history
shift-f1,f2,f3 - archive management commands
shift-f10 - show the last menu command
ctrl-\ - back to root
shift-enter in the drive menu - show root directory in explorer
ctrl-pgdn - enter in an archive/especially SFX
ctrl-g - run command on selected files, like “rar32 m !.!.rar !.!” to rar each file in its own archive
alt-ins - screen grabber
ctrl-“gray .” - record a keyboard macro
alt-del - wipe file, overwrite with 0, trunicate, rename to a temp name and delete.
ctrl-w - task list
ctrl-tab F12 - switch panes (screens) inside of far
ctrl-f full file name into the command line
alt shift ins full file name into clipboard for selected files
ctrl alt ins unc names into clipboard of the selected files
ctrl ins name into clipboard of the selected files if no cmd line
ctrl shift ins name into clipboard of the selected files always
ctrl m restore previous selection
ctrl enter in quick search (alt-letter) selects file and moves to the next
shift enter in history selects an item not changing its positions
In the drive menu - Shift - Del to disconnect Flash, Del remove a CD.
Ctrl-. to start recording macro. Ctrl-. again to end and assign a key
To erase a macro do Ctrl-. twice then use the key you want to erase.

FAR Shortcuts Printout

(source)