Intermediate Sudoku Strategies: Hidden Singles, Pairs & Pointing Patterns

You've mastered the basics — scanning, cross-hatching, pencil marks — and Easy puzzles feel routine. But Medium puzzles keep stalling halfway. Welcome to the intermediate plateau. The five patterns in this guide (naked singles, hidden singles, naked pairs, hidden pairs, and pointing pairs) are the exact tools that break it. Learn to spot them and Hard puzzles come into reach.

A quick note before we start: these strategies assume you're using pencil marks. If you haven't been marking candidates, go back and build that habit first — these patterns are nearly invisible without it.

Naked Singles

A naked single is the simplest intermediate move: a cell whose pencil marks have been whittled down to exactly one candidate. It's "naked" because there's nothing hiding — the answer sits there in plain sight.

Cell r4c6 shows pencil marks: { 7 }
→ r4c6 = 7. Fill it in.

Naked singles appear as a result of your marks, not something you hunt for directly. The skill is maintenance: every time you place a number, update the marks in its row, column, and box, then re-scan for new naked singles. Chains of these — place, update, spot, repeat — solve a huge fraction of Medium puzzles on their own.

Hidden Singles

A hidden single is sneakier. The cell has several candidates, but within its row, column, or box, one of those digits appears as a candidate in no other cell. The digit is "hidden" among the cell's other marks, but the unit reveals it.

Row 7's empty cells and their candidates:
  c1:{3,8}  c3:{2,8}  c4:{3,6}  c7:{2,6}  c9:{2,3}

Digit 8 appears only in c1 → r7c1 = 8 (a hidden single in the row),
even though r7c1 also lists 3 as a candidate.

How to hunt them: pick a unit (row, column, or box) and a digit, then count how many cells in that unit list the digit as a candidate. If the count is one, you've found a hidden single. Working digit-by-digit through each unit is slower than scanning, but it's where Medium puzzles actually get solved.

Naked single vs. hidden single, in one line: a naked single is a cell with one candidate; a hidden single is a digit with one home.

Naked Pairs

A naked pair happens when two cells in the same unit contain exactly the same two candidates — and nothing else. Since those two digits must occupy those two cells (in some order), you can delete both digits from every other cell in the unit.

Row 3 (relevant cells):
  c2:{4,9}  c5:{4,9}  c7:{4,6,9}  c8:{1,4,9}

c2 and c5 form a naked pair on {4,9}.
→ Remove 4 and 9 from c7 and c8:
  c7:{6}  c8:{1}   ← two new naked singles!

Notice the payoff: the pair itself didn't give you a placement, but the eliminations it unlocked cracked two other cells. That's typical — intermediate techniques are elimination engines, and the placements fall out afterward.

The pattern generalizes: a naked triple is three cells in a unit sharing exactly three candidates (delete those digits from the rest of the unit), and likewise for quads. Triples show up; quads are rare enough to just enjoy when they appear.

Hidden Pairs

A hidden pair is the mirror image: two digits appear as candidates in exactly the same two cells of a unit, even though those cells list other candidates too. Those two cells must contain those two digits, so every other candidate can be erased from both cells.

Box 5 (center box), relevant cells:
  r4c4:{2,5,7}  r6c6:{5,7,9}

Digits 5 and 7 appear nowhere else in this box.
→ Hidden pair {5,7} in r4c4 and r6c6.
→ r4c4 becomes {5,7}, r6c6 becomes {5,7}.

Hidden pairs are harder to spot than naked pairs because the extra candidates camouflage them. The hunting method: in a unit, look for two digits that keep showing up in the same two cells. With practice, your eyes learn the shape of it.

Pointing Pairs (and Triples)

A pointing pair bridges boxes and lines. When a digit's candidates inside a 3×3 box are all confined to a single row (or column), that digit is "pointing" — it must go in that row somewhere within the box, so it can't appear anywhere else in that row outside the box. Delete it from the rest of the row.

Top-left box: digit 6 appears as a candidate only in r1c1, r1c2, r1c3
(all in row 1).
→ 6 must occupy one of those three cells → delete 6 from
   r1c4, r1c5, r1c6, r1c7, r1c8, r1c9.

The same logic works with three cells (a pointing triple) and with columns instead of rows. Pointing patterns are satisfying because one observation can trigger a cascade of eliminations across the grid.

A Practice Routine for These Patterns

Don't try to learn all five at once. Spend one solving session on each:

1. Session 1: Naked singles — focus purely on mark maintenance.
2. Session 2: Hidden singles — hunt digit-by-digit through units.
3. Session 3: Naked pairs — scan rows and boxes for twin candidate sets.
4. Session 4: Hidden pairs and pointing pairs — the camouflaged ones.

Play Medium puzzles on SudokuPuzzle.pro with notes mode on, and give yourself permission to be slow. Pattern recognition is a muscle; the reps are the whole game. When these five feel automatic, the advanced techniques — X-Wing, Swordfish, and coloring — are waiting.

Put these strategies to work on SudokuPuzzle.pro — free unlimited puzzles, and the Daily Challenge (Hard, every day) is the perfect training ground for your new skills.