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Sudoku Solving Techniques
Every Sudoku puzzle is solved with the same small toolkit, applied in a smart order. The techniques below form a ladder: at the bottom are simple scanning moves that place a digit outright, and at the top are pattern-spotting methods that let you erase candidates you could never place directly. If you are new to the game, start with the basic rules and come back once the one-rule-per-unit idea feels natural. As puzzles get harder, you stop placing numbers and start eliminating possibilities, so the advanced techniques all rely on pencil marks (also called candidates): the small notes of every digit that could still legally go in a cell. Keep those marks accurate and the patterns below reveal themselves. And because a Samurai Sudoku is really five overlapping 9x9 grids, every one of these techniques applies inside each grid exactly as it does in a standalone puzzle.
Naked Single
Only one digit can go here. Every other number already appears in this cell's row, column, or box, so it's forced. A naked single is the most basic placement in Sudoku, and it is the payoff of good pencil marking: when a cell's candidate list collapses to a single number, that number is the answer, no reasoning required. Look for naked singles constantly, especially right after you place a digit or clear candidates with a more advanced move, because one placement often triggers a chain of them. Scan cells in the most crowded rows, columns, and boxes first, since a cell hemmed in by many filled neighbors is the likeliest place for its options to shrink down to one.
Hidden Single
Look at a whole row, column, or box: a digit can only fit in one cell, even though that cell looks like it has other options. Where a naked single is about one cell with one candidate, a hidden single is about one unit with one home for a particular digit. The target cell may still list several candidates, which is exactly why it hides in plain sight. To find them, pick a digit and ask, "Within this box, which cells could hold a 7?" If only one survives after crossing off the row and column conflicts, that cell must be 7 no matter what else it seemed to allow. Hidden singles are the workhorse of easy and medium puzzles, and scanning digit by digit through every box will uncover most of them.
Locked Candidates (Pointing Pairs)
Inside one box, a digit is pinned to a single row or column. That lets you erase it from the rest of that line. This is your first true elimination technique. Suppose the only cells in a box that can hold a 4 all sit in the same row. You cannot yet say which cell it is, but you do know the box's 4 lives somewhere in that row, so no other cell in that row (outside the box) can be a 4. Erase 4 from those cells. The mirror case, where the candidates line up in a column, works the same way. Look for pointing pairs whenever a digit appears just two or three times in a box and those appearances share a line. The eliminations they create frequently open up a hidden or naked single elsewhere.
Naked Pair
Two cells in a unit share the exact same two candidates. Those two digits belong to that pair, so they can be removed from every other cell in the unit. If two cells in a row both show only {3, 8} and nothing else, then between them they will consume the 3 and the 8 for that row, in some order. No other cell in that row can be 3 or 8, so you strike those two digits from the rest of the row. The same logic holds within a column or a box. The key requirement is that both cells contain exactly those two candidates and no others. Naked pairs are easy to miss because you have to notice two cells matching each other rather than reading a single cell, so it helps to glance along each unit for twin candidate lists.
Hidden Pair
Two digits can only land in the same two cells of a unit. Those cells must hold that pair, so all their other candidates fall away. A hidden pair is the naked pair's mirror image. Instead of two cells wearing only two candidates, you find two digits that appear nowhere else in the unit except in the same two cells. Say the digits 2 and 6 can each go in only cells A and B of a box, though both cells also list several other candidates. Because 2 and 6 have nowhere else to live, they must occupy A and B between them, which means every other candidate in A and B can be deleted. Hidden pairs are harder to spot than naked ones, so hunt for them by counting how many times each digit can be placed in a unit and flagging digits that appear in exactly two matching cells.
Naked Triple
Three cells together use only three candidates between them. Those digits are locked to the trio and cleared from the rest of the unit. A naked triple extends the naked pair idea to three cells and three digits, with a useful twist: not every cell needs all three candidates. Cells listing {1, 5}, {5, 9}, and {1, 9}, for example, still form a valid triple on the digits {1, 5, 9}, because those three digits will fill those three cells among themselves. Whenever three cells in a unit draw only from the same pool of three candidates, no other cell in that unit can use any of those three digits. These are worth checking on tougher puzzles where pairs alone stall out, and combinations of two-candidate and three-candidate cells are the usual shape.
X-Wing
A digit lines up in a rectangle across two rows and two columns. That pattern means it can't appear elsewhere in those columns (or rows). Picture a candidate, say 5, that can go in exactly two cells of one row and exactly two cells of another row, with all four cells sharing the same two columns. Those four cells form the corners of a rectangle. In each row the 5 must sit in one of its two corners, and the geometry forces the solution into one of two diagonals, so both of those columns will get their 5 from within the rectangle. That means 5 can be erased from every other cell in those two columns. The pattern also works with the roles of rows and columns swapped. The X-Wing is the gateway to fish patterns; for a fuller walkthrough with examples, see our dedicated X-Wing guide.
XY-Wing
Three cells linked by shared candidates form a pivot and two pincers. Any cell that sees both pincers can't hold the shared digit. The XY-Wing uses three cells that each hold exactly two candidates. One cell is the pivot, holding candidates X and Y. It connects to one pincer holding X and Z, and to another pincer holding Y and Z, where "connects" means they share a row, column, or box. Whichever digit the pivot turns out to be, one of the two pincers is forced to become Z. So any cell that can see both pincers is guaranteed to have a Z somewhere among them and cannot itself be Z. Erase Z from those seen cells. XY-Wings are powerful precisely because the eliminations can happen far from the pattern itself, so trace the lines of sight carefully.
Swordfish
Like an X-Wing but bigger. A digit's positions across three rows and three columns form a pattern that eliminates it elsewhere. Where the X-Wing uses two rows and two columns, the Swordfish uses three of each. Take a candidate that appears in only two or three cells in each of three rows, and arrange it so all those cells fall within the same three columns. The digit is then confined to those three columns across those three rows, so it can be removed from any other cell in those columns. As with the X-Wing, the pattern works equally well starting from three columns and eliminating along rows. Swordfish are rare and demand clean, complete pencil marks to see, but on genuinely hard grids they crack positions that nothing simpler can.
Worked through top to bottom, these nine techniques cover the overwhelming majority of moves in any classic or Samurai puzzle. Reach for scanning first, lean on locked candidates and pairs to break the mid-game open, and save the fish and wing patterns for when the easy moves dry up. The real skill is not memorizing every pattern but knowing which one to try next, and that judgment comes with practice. If you want a coach while you learn, Samuraiku offers smart hints that name the exact technique each move uses, so you can recognize the pattern yourself the next time it appears. Keep your candidates tidy, climb the ladder in order, and even the most stubborn grid becomes a sequence of small, solvable steps.