Introduction
This last weekend, I took part in SEATST (Southeast Asia Team Selection Test) 2026. A few people (YSH2020 and Tyx2019) have posted blogs on the contest.
About SEATST
SEATST is a IOI format (2 days, 3 problems in 5 hours on each day) contest made in 2025 that "replaced APIO as a crucial component of IOI selection in Singapore." (this statement is directly quoted from the SEATST website found here).
Looking at my APIO scores for these 2 years and my SEATST scores, I believe I am one of the largest beneficiaries for the shift away from APIO towards SEATST. Here are my scores:
- APIO 2025: 87/300, 10th in SG
- SEATST 2025: 380/600, 3rd in SG
- APIO 2026: 13.5/300, 21st in SG (I know my strategy was kinda screwed but whatever)
- SEATST 2026: 419/600, 4th in SG
My experience this year
I had quite an interesting experience in this year's SEATST, best summed up by my score distribution:
(300 on day 1, 119 on day 2)
This is also why I'm only doing editorial for day 1.
The contest quality was actually pretty good. Just that on day 2 I spent too long debugging and failing to spot the bug.
Problems
The problems can be found here. There are English translations on the website.
The following includes abridged problem statements and ideas for each problem.
Problem 1A (Two Exams)
Abridged statement: Given positive integer $$$N$$$ and two permutations $$$A$$$ and $$$B$$$ of $$$[0,1,2,\cdots,N-1]$$$, a permutation $$$P$$$ of $$$[0,1,2,\cdots,N-1]$$$ is valid if for all $$$0 \le i \le N-1$$$, one of the following hold:
- For all $$$j$$$ such that $$$P[j] \lt P[i]$$$, $$$A[j] \lt A[i]$$$
- For all $$$j$$$ such that $$$P[j] \lt P[i]$$$, $$$B[j] \lt B[i]$$$
Minimise the largest value of $$$P[i] - i$$$.
