On Wednesday, 12 March, Sutton Grammar School finished first in the 2025 Reply Code Teen Hack the Code Challenge.

The Reply Hack The Code Challenge Teen Edition is an online, team-based coding and security competition for high school students aged 14 to19, where teams solve 5 algorithm-based problems, including a bonus CTF (Capture the Flag) challenge to potentially double points. 

More than 160 SGS students in Years 9 to 13 took part in the competition. SGS finished with 390,100 points. 

Below, two of our Year 13 senior coders, Jidneya Desale and Sirius Chan share their experiences and the challenges they faced during the competition.

Jidneya Desale -

The Reply Code Challenge is an international competition in which teams have six hours to solve computing puzzles and cybersecurity challenges. This year, our team was determined to top the school's leaderboard after narrowly missing the mark in previous years.

We carefully analysed problems, developing strategies that evolved from brute force to elegant solutions requiring logical thinking. Problems ranged from detecting malicious commands in user input to being able to solve sudoku tables that had shifted rows and columns. Programming these solutions demanded optimization and thorough testing, and high levels techniques such as dynamic programming and backtracking. The cybersecurity challenges required technical web hacking knowledge but were equally rewarding to solve. Despite the complexity of these situations, which demand not only technical knowledge but also resilience, when you finally get the solutions, it is a very rewarding feeling that helps boost not only your team's ranking but also the school's ranking.  

After six intellectually demanding hours, the challenge ended with 7,423 submissions from 542 international teams. Our school earned 390,100 points—an achievement that reflects our computer science department's dedication and should make our entire school proud.

Sirius Chan -

One task involves solving a 36x36 Sudoku grid, which normally takes a computer a fraction of a second to complete. However, some numbers in the starting grid were swapped to different positions, so the grid had to be "corrected" before the solving could begin. There was only one slight issue - there are more possible arrangements of grids than there are atoms in the visible universe, and we had no better way to identify the correct arrangement than to look through each of them! Whilst the grid remained unsolved during the challenge, various approaches were discussed in the days following the event.