Solving easy classic sudoku

Easy classic sudoku is the tier built around two moves — the naked single and the hidden single — and a steady scanning rhythm that finds them. Most easy puzzles solve in fifteen to twenty-five minutes once the rhythm clicks, and most beginners get there within a week or two of regular play. There are no chains at this tier, no patterns spanning multiple regions, no candidate notes you have to maintain. The puzzle yields cell by cell.

The two moves that fire at this tier

The two techniques that solve almost every easy puzzle — naked singles and hidden singles — get a full treatment in our piece on the two moves that solve most easy puzzles. The short version, repeated here for orientation: a naked single is the cell where eight of the nine digits have already been ruled out by the row, column, and box, leaving exactly one. A hidden single is the cell that's the only one in a region — a row, a column, or a box — where a particular digit can go. These are the only techniques you'll need at easy. Anything more involved — locked candidates, naked pairs, hidden pairs — starts at medium.

The scanning rhythm

The way to solve an easy puzzle is to find these moves one at a time by scanning. After every digit you place, check the row, column, and box you just changed. The next single is usually one of those three regions; placing one digit eliminates that digit from three regions at once, which often opens up the next single immediately. Don't drift across the grid looking for moves — let the cell you just filled in tell you where to look next. That's the rhythm easy rewards, and once you settle into it, an easy puzzle solves in fifteen minutes without conscious effort.

On a fresh grid, the standard approach is to scan by digit. Pick whichever digit appears most often in the givens, and check every box for hidden singles of that digit. Then move to the next digit. This isn't elegant, but it's mechanical and it works — most easy puzzles will have several hidden singles in the first pass. Once those are placed, the naked singles start cascading.

Where to look when scans stall

Box 5, the centre box, is statistically the most-touched region on the grid. More rows and columns pass through it than through any other box, so it accumulates eliminations from elsewhere on the grid faster than any other box. When scans elsewhere stall, the centre box is often where the next move is hiding. This holds at every tier, but it's especially true at easy where the moves are simple enough that where is more of the puzzle than what.

Pencil marks aren't necessary at easy. Some cells resolve faster than you can write notes for them, and the others resolve before you'd have needed the notes anyway. You're welcome to use them — people do, especially if they're learning the notation for later — but they don't earn their place at this level. Our piece on pencil marks without the clutter goes deeper if you're curious about how to use them at higher tiers.

When easy stalls

Easy stalls in one of two ways, and the fixes are mechanical rather than tactical.

The most common is tile-blindness. You've placed several digits, broken your scanning rhythm, and stopped checking regions systematically. The next single exists; you're just not looking in the right region for it. The fix is to pick a region you haven't checked recently and scan it digit by digit — after thirty seconds of structured scanning, the next move usually appears.

The second pattern is the false-positive on a placed digit. You see a 7 in a particular box and your eye reads the row's 7-question as settled, when actually the 7 is in a different box and the row's 7 is still unplaced. The fix is to slow down — when you check whether a digit is in a row, count the actual cells, don't just glance. Easy has enough givens that this rarely causes errors, but it does cause stalls, especially toward the end of the solve when the grid looks mostly done and your attention is winding down.

Two habits to drop early

Guessing. Easy puzzles are designed to be fully solvable by logic alone — if you can't see the next move, the next move exists and you haven't found it yet. A wrong guess gets discovered ten cells later when something doesn't fit, and at that point unwinding is painful. Coming back to the puzzle after a minute's break almost always reveals the cell that was hiding in plain sight. That's the right response to a stall, not a guess.

Speed-solving on the first hundred puzzles. Easy is the tier where the rhythm matters more than the time. Solving a hundred easy puzzles in fifteen-minute blocks each is better practice than rushing twenty-five of them in five-minute blocks, even though the total puzzle count is lower. The goal at easy is to make the scanning rhythm automatic; once it is, the speed comes free. Trying for speed before the rhythm is in place produces stalls, errors, and frustration in roughly equal measure.

At some point the puzzles start solving themselves. The rhythm becomes automatic, you stop noticing the techniques fire, and the only conscious effort is keeping pace. That's the signal you're ready for medium, where the first moves that ask you to combine two regions show up — the territory walked through in your first medium puzzle. Easy is worth coming back to occasionally though, the puzzle equivalent of a long quiet walk after a stretch of harder reading.