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Rush Hour & Unblock: Sliding-Block Strategy
A sliding-block puzzle looks like a parking-lot traffic jam: one special block needs to reach the exit, and a crowd of cars and trucks sits in the way, each one stuck moving only along its own line. The temptation is to start shoving pieces around and hope a path opens up - but that usually just builds a new jam somewhere else. The faster, calmer approach is to read the board first and slide second. This guide shows you how to trace the exact chain of blockers between the target and the exit, free them in the right order, and leave every piece that is not in your way completely alone.
How a sliding-block puzzle works
Every piece on the board is a block one square wide and two or three squares long. The rule is simple but strict: a block can only slide along the line it already lies on. A block lying flat moves left and right; a block standing tall moves up and down. None of them ever turn, and none of them ever jump over another piece. A block can only move into empty squares directly in front of it.
One block is your target - usually a special-coloured one - and one edge of the board has a gap that is the exit. Your only job is to clear a straight, empty path along the target's line so it can slide out through that gap. Everything else on the board exists purely to get in the way. Once you see the puzzle as "free this one lane" rather than "tidy the whole board," it stops feeling like chaos and starts feeling like a plan.
Read the board before you touch a piece
The single biggest improvement you can make is to look before you slide. Find your target block, then look straight along its line toward the exit and notice every piece sitting between it and the gap. Those pieces - and only those pieces - are the ones standing between you and a win. Everything off to the side is scenery for now.
This row or column of obstacles is the blocking chain. A tidy puzzle might have just one block in the way; a hard one might have three or four stacked along the exit lane. Counting them tells you how much work the puzzle really is, and it stops you from wandering off to rearrange a corner that was never the problem.
Trace the lane first. Before your first move on any board, run your finger along the target's path to the exit and name each block in the way. In Mochi Unblock the exit sits on one edge and the target slides straight toward it, so the blocking chain is always whatever pieces share that one lane. Spotting them up front turns a scary board into a short to-do list.
Work backwards from the exit
Here is the idea that makes hard boards solvable: don't ask "what can I move right now?" - ask "what has to move for the target to escape?" Then, for each blocker, ask the same question again. You are working backwards from the goal instead of forwards from the mess.
Start with the blocker nearest the exit and look at how it can clear the lane. A standing block has to slide up or down; a flat block has to slide left or right. Now check whether the squares it needs to move into are empty. Often they are not - which means a second piece is blocking your blocker. That piece becomes your new problem, and you trace its escape the same way. Following this thread usually leads you to a block that genuinely can move right now, with nothing in its path. That is where you begin, and each move you make frees up the next link in the chain.
This backward chase is exactly how you avoid the most common trap: moving a piece because you can, not because it helps. Every move should be in service of freeing a specific blocker. If a slide doesn't make room for some piece you have already identified as in the way, it is almost certainly wasted - or worse, it parks a block where you will have to dig it out again later.
Clear the exit lane and keep it clear
As you free each blocker, you have to send it somewhere - and where you send it matters as much as that you moved it. A standing block lifted out of the exit lane should be parked where it won't drift back into the target's path; a flat block slid aside should end up clear of the lane, not just barely out of it. The exit lane is sacred. Once a square in that lane is empty, treat it as off-limits and never slide another piece into it.
It helps to think about the empty squares as your real resource. There are only ever a few gaps on the board, and every move borrows one. Before you commit to shifting a big truck, glance at where the empty space will end up - if pushing one block simply transfers the jam to the exit lane, you have gone backwards. The boards that feel impossible are usually the ones where the only free squares are all clustered in one corner, far from where you need room. Freeing up space near the exit lane early gives every later move somewhere to go.
A step-by-step routine for any board
Put it together and you have a method that works the same way on an easy board and a brutal one:
- Find the target and the exit. Note which line the target sits on and which edge it needs to reach.
- Trace the blocking chain. Look along the exit lane and name every piece between the target and the gap. Ignore everything else.
- Work backwards from the exit blocker. For the piece nearest the exit, ask what direction it must move and whether those squares are free. If not, follow the new blocker the same way.
- Start at the loose end. The chain leads you to a block that can move right now - begin there and clear blockers in the order that opens space for the next one.
- Protect the exit lane. As each square in the target's path empties, keep it empty. Don't slide a freed piece into the very lane you are trying to open.
- Slide the target out. Once the lane is clear all the way to the gap, send the target home in one smooth run.
Common mistakes that stall a board
- Shuffling pieces that aren't in the way. If a block doesn't sit on the target's lane or block something that does, leave it alone. Moving idle pieces only eats up the empty squares you need elsewhere.
- Thinking forwards instead of backwards. Asking "what can I move?" leads to aimless sliding. Ask "what must move for the target to escape?" and follow that thread to a piece that is actually free.
- Refilling the exit lane. Clearing a square and then parking another block in it is the classic way to undo your own progress. Once a lane square is empty, keep it empty.
- Parking a freed block badly. When you slide a blocker out of the way, send it somewhere it will stay out of the way - not one square clear, where the next move shoves it right back.
- Hoarding empty space in a corner. If all the gaps end up far from the exit, every move gets cramped. Keep some breathing room near the lane you are opening.
Use undo as a thinking tool. Stuck boards reward experiment. Try freeing the chain, and if the exit lane jams up, step back a move or two and clear the blockers in a different order. Mochi Unblock lets you reset and try again without penalty, so a board that looks hopeless is just one you haven't traced the right way yet.
Where to go next
The fastest way to make this method automatic is to play a few boards while narrating the chain to yourself: target, exit, blockers, then work backwards. Mochi Unblock is built exactly for that kind of practice - tap or drag a block and it slides along its own line, the exit is always in plain view, and the puzzles ramp up gently so the blocking chains grow as your eye gets sharper. If you enjoy the slow, satisfying logic of moving one piece to free another, try our guide on winning at Sokoban next, then the classic sliding picture puzzle for a different twist on the same single-gap idea.