Hop'n'Pop

Polypop 4×4 — ULL fixed-pin solve visualiser
U pentomino + L triomino + L tetromino · one fixed non-corner pin · choose two of the other three voids

Choose a starting configuration

Fixed pin: row 1, column 3 (top row, third cell). The other two pins are chosen from the remaining three voids.
180Solvable configurations
0Unsolvable configurations
29Longest shortest solution
21.13Average shortest moves

Move controls

Initial layout0 / 0

A move lifts one piece and places it in a legal position. The moved piece may rotate or flip. Pins act only when that piece is placed; stationary pieces do not change.

Board state

U5 L3 L4lighter related shade = piece turned upside down movable pin fixed pin bump up bump down

Configuration audit

The fixed pin is at row 1, column 3. “Packing orientation” describes the orientation relative to the canonical packing; the board and fixed pin do not move. There are 60 eligible oriented piece packings; each has three choices for the other two pins, giving 180 configurations. All 180 are solvable.

Bump-back notes

A ★ in the pin-choice dropdown marks a configuration whose shortest solution includes at least one bump being pushed back UP after it had already reached DOWN. There are 15 such configurations out of 180 (8 involve U5, 7 involve L4, and none involve L3). The bump-back occurs between moves 5 and 19. No configuration requires more than one bump-back.

A ★ beside a packing class means at least one of its pin choices has this feature. The ★ beside an individual “Leave … unpinned” choice is the exact configuration marker.