Got a Wrong Answer in judging but don't know why? | How to hack yourself

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When to use this:

getting Wrong Answer but don't know why, or in a non-real-time-feedback contest and to check whether your code is right
have a program to generate random input data
for standard problems: have a code that will not output the wrong answer (time limit exceedings are acceptable)
for special judge problems (example: problems that allow you to output one of the multiple answers): have a program to check if the answer is right
for interactive problems: too weak in coding to know how to use :( if you know, comment below plz ˋ( ° ▽、° )
if you are in a contest: make sure you have enough time to write these codes (data generator, bruteforce, checker, etc.)

You should have these files below in the same folder:

1.cpp (or other languages): Your code that got Wrong answer.
For standard problems: std.cpp (or other languages): Code that will not output the wrong answer
For special judge problems: checker.cpp (or other languages): To check if your output is right, returns 0 in main() if wrong, and returns 1 if correct
gen_data.cpp (or other languages): To generate random input data
hacker.sh/bat (or other languages that can run bash/cmd command): main program

Details of implementation:

For gen_data.cpp: use mt19937 and chrono::high_resolution_clock().now().time_since_epoch().count() to generate random integer instead of rand() and srand(time(0)). Tutorial of mt19937

For Windows, standard problems, the hacker.cpp: (sorry for not knowing much about batch)

code

#include <bits/stdc++.h>
using namespace std;

int main() {
	// ↓ compile your code here ↓
	// ↑ compile your code here ↑
	int i = 0;
	do {
		system("gen_data.exe > in.txt");
		system("1.exe < in.txt > out.txt");
		system("std.exe < in.txt > ans.txt");
		cout << ++i << endl;
	} while (!system("fc out.txt ans.txt"));
	cout << "in: " << endl;
	system("type in.txt");
	cout << "ans: " << endl;
	system("type ans.txt");
	cout << "out: " << endl;
	system("type out.txt");
	return 0;
}

For Windows, special judge problems, the hacker.cpp:

code

#include <bits/stdc++.h>
using namespace std;

int main() {
	// ↓ compile your code here ↓
	// ↑ compile your code here ↑
	int i = 0;
	do {
		system("gen_data.exe > in.txt");
		system("1.exe < in.txt > out.txt");
		cout << ++i << endl;
	} while (system("checker.exe"));
	cout << "in: " << endl;
	system("type in.txt");
	cout << "out: " << endl;
	system("type out.txt");
	return 0;
}

For Linux/macOS, standard problems, the hacker.sh:

code

if ! [ -e 1.cpp ]; then
    echo "file doesn't exist"
    exit
fi
# ↓ compile your code here ↓
shopt -s expand_aliases 
alias comp_cpp="g++ -O3 -Wall -Wextra -Wshadow -std=c++14"
comp_cpp std.cpp -o std.out
comp_cpp 1.cpp -o 1.out
comp_cpp gen_data.cpp -o gen_data
# ↑ compile your code here ↑
i=0
while true
do
    ./gen_data > in
    ./std.out < in > ans
    ./1.out < in > out
    diff -b -B ans out > dif
    if [  -s ./dif ]; then
        echo $i
        echo "hack:"
	cat in
        echo "ans:"
        cat ans
        echo "out:"
        cat out
        rm -f 1.out bruteforce.out gen_data dif
	exit
    else
        let i++
        echo $i
    fi
done

For Linux/macOS, special judge problems, the hacker.sh:

code

if ! [ -e 1.cpp ]; then
    echo "file doesn't exist"
    exit
fi
# ↓ compile your code here ↓
shopt -s expand_aliases 
alias comp_cpp="g++ -O3 -Wall -Wextra -Wshadow -std=c++14"
comp_cpp 1.cpp -o 1.out
comp_cpp gen_data.cpp -o gen_data
comp_cpp checker.cpp -o checker
# ↑ compile your code here ↑
i=0
while true
do
    ./gen_data > in
    ./1.out < in > out
    diff -b -B ans out > dif
    if [  ! checker ]; then
        echo $i
        echo "hack:"
	cat in
        echo "out:"
        cat out
        rm -f 1.out bruteforce.out gen_data dif
	exit
    else
        let i++
        echo $i
    fi
done

The main usage of this is to generate small-scale data for debugging.

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