A major week

Meta Hacker Cup 2025 Round 1 was the main event of last week (problems, results, top 5 on the left, analysis). As usual in the early Hacker Cup rounds, one has to balance the speed against the amount of effort you spend to test your own solutions before attempting to submit them. There is just one attempt per problem, and the submission result is only revealed after the round ends (a pretty unique setup for today's contests, but one that I think makes the competition more exciting and emphasizes the useful testing skills!), and at the same time you only need to be in top n to advance, your score does not matter for the future rounds. It does matter for the bragging rights though, so well done to Geothermal on being much faster than everybody else!

The Hacker Cup is now the "Major Individual Competition" (according to cphof) that was held the most years among those still happening, this one is the 15th edition! TopCoder Open/Invitational is still in the overall lead with 22 editions, but that number is not going to increase further. Huge thanks to the organizers for putting it together year after year, and I'm looking forward to participating in the next 15, and of course to you bringing back the onsite finals :)

Problem D was quite nice, and you can also solve it as a math problem without any computer help. You are given a string of 0s and 1s (check out the original problem statement for the more colorful story!) of length <=600000. Two players are playing a game, making moves in turns. On each move of the first player, they erase any prefix of the string that ends with a 0. On each move of the second player, they erase any suffix of the string that starts with a 1. The player who cannot make a move loses. Who will win if both play optimally?

Thanks for reading, and check back next week!