Frequently asked questions
Can a shuffle ever be unsolvable?
No. Half of all random tile arrangements are mathematically unsolvable, so this game never places tiles at random — it starts from the solved board and slides tiles backwards hundreds of times. Anything reached by legal moves can always be solved by legal moves.
Any tips for solving faster?
Solve row by row: finish the top row first, then the next, without breaking completed rows. For the last two rows, work column by column from the left, placing the two tiles of each column together. The final 2×2 corner then resolves with a simple rotation.
What is a good time for the 4×4?
Casual players typically finish a 4×4 in 2–5 minutes. Under a minute is genuinely fast, and speedsolvers who practice finger tricks can go under 30 seconds. Beating your own best time is the most satisfying benchmark.
Who invented the 15 puzzle?
The craze began around 1880, and the invention is generally credited to Noyes Chapman, a New York postmaster. Puzzle showman Sam Loyd later claimed it and famously offered $1,000 for solving a version with tiles 14 and 15 swapped — a prize that was safe forever, because that arrangement is mathematically impossible.
How many moves does a perfect solution take?
For the classic 4×4, the hardest positions need exactly 80 single-tile moves — the puzzle's so-called God's number, proven by computer search. Most shuffles need fewer, and human solvers typically use far more, since move-efficient solving means planning several tiles at once instead of fixing one at a time.
Why is the 5×5 so much harder than the 3×3?
Every size jump multiplies the possibilities enormously: the 3×3 has 181,440 reachable positions, the 4×4 over ten trillion, and the 5×5 vastly more still. Bigger boards also mean longer solutions and more completed rows to protect while you work, so patience and a solid row-by-row method matter far more.