1. Choose a fictional station
These are number puzzles, not real station layouts. Numbers are sorted and each appears once. The hidden answer stays the same until you change or restart the mission.
Candidate board
Solid border = still possible. Dashed and crossed out = eliminated. A found number is marked with ✓. The text summary above gives the same information.
Your search history
No guesses yet. Try a number or use the midpoint hint.
2. Why the middle helps
A linear search checks numbers one at a time. With 63 numbers, it might need 63 guesses. A binary search chooses the middle of the remaining sorted numbers. A higher/lower clue discards that guess and the entire impossible side.
With 63 possibilities, midpoint guessing needs at most 6 guesses, including the final successful guess. It might finish sooner! The guarantee is a worst-case bound, not a score you must reach. Arbitrary guesses can take longer.
Try the same mission twice: first check the lowest remaining number each time, then restart and use midpoints. The target is unchanged, so this is a strategy comparison, not a fresh mystery.
See the algorithm (pseudocode)
low = 1; high = largest platform number
while low <= high:
middle = round DOWN ((low + high) / 2)
if middle is the target: finish
if target is higher: low = middle + 1
otherwise: high = middle - 1Rounding down chooses one of the two middle numbers when there is an even number of candidates. Either middle works if you update the boundaries correctly.
Explain it to someone
- Why can you cross out every number below a guess when the clue says higher?
- Would the same method work on unsorted wagon labels? Why not?
- What happens when only one candidate remains? You still need to guess it to finish.
No account, saved scores, personal information or input uploads. Reloading starts at the small stop. Answers are in the browser code; this is learning, not a secure competition.