Just Shikaku

Seven techniques stand between guessing at rectangles and reading a board at a glance. Just Shikaku names them, teaches each one on a real position, and then proves you know them. Shikaku hands you a grid of numbers. You carve it into rectangles until every number sits in a rectangle of exactly that many cells. The rules take a minute. Playing well takes arguments, ones with names like Prime Strips, Lone Reacher, and No Orphans, and those arguments are what this app is actually about. WHAT NO OTHER SHIKAKU HAS - A curriculum. Seven named techniques, each with its own lesson on a board where that technique is the next move. - Hints that argue. Ask for help and the reasoning climbs a ladder: a nudge, then the technique's name, then the full argument drawn on your board: the candidates that could work, the ones that die, the cell that decides it. The app can lay the rectangle for you, but that is the ladder's last rung and it applies exactly one argued move. Your solve stays yours. - A daily that teaches. Every player in the world gets the same room, and each day's room is built around one named technique. Solve it and your streak grows; solve it unaided and that technique's mastery grows with it. - Proof behind every board. Before a puzzle reaches you, the engine has verified it has exactly one solution and that the taught techniques are enough to reach it. Guessing is never required, on any board, at any difficulty. - Mastery you earn by understanding. Each correct rectangle you lay without help is checked against the solver's own derivation, and the hardest technique in that reasoning gets the credit. Seven seals fill as you learn; speed is never the score. - The proof. When you finish a room, the app replays your own solve and grades every rectangle: worked out, laid by a hint, or a leap beyond what the lessons cover. No other puzzle app can tell you which of your own moves were reasoned. WAYS TO PLAY Today's room is the same board for everyone, built around one named technique, with a streak and a seal for a full week. The Climb sends room after room up the difficulty ladder. Spot It serves ten real mid-game positions where one technique is the move. Timed drills take a technique's board cold, and you can ask for a whole board generated to need the technique you picked. The Climb and Spot It end on three wrong rectangles and neither has a clock, because accuracy is the game, not speed. Every mode explains itself: Learn lists them all, and each one carries the same explanation behind an info button. BUILT LIKE AN INSTRUMENT Drawing rectangles is the whole interface, so it has to be right: the drag anchors where your finger lands, a live count shows the cells you have against the cells you need, the board's border is forgiving to edge-of-screen fingers, and redrawing over a rectangle simply replaces it. Timed drills rehearse one technique on a cold board. Statistics show your streak, your solve history, and how your hint use falls as the techniques land. One committed look: a dark room, green rectangles, drawn digits. No themes, no confetti, and the only red in the game is the ink the teaching uses. FREE FOREVER The rules, the first two technique lessons, today's room with its streak and weekly seal, The Climb, 5x5 and 7x7 boards at every difficulty including the hardest, best times, and an error check. THE WHOLE ROOM, ONCE A single purchase adds the five remaining lessons, the timed drills and Spot It, the full hint ladder with the drawn argument, 10x10 and 12x12 boards, and the complete statistics. No subscription. No ads. Hints are never a currency. Everything works offline.