Easy Sudoku Techniques

Easy puzzles start with 38 or more pre-filled cells — nearly half the grid. That density means straightforward moves are always available. You should be able to solve every easy puzzle using only three techniques: cross-hatching, last remaining cell, and naked singles. Guessing is never required on an easy puzzle; if you feel the urge, look again.

The goal of easy puzzles is to build fluency with fundamentals so they become automatic. Once your eye spots a naked single without conscious effort, you are ready for medium difficulty and the techniques that build on these foundations.

Cross-hatching is the first technique every solver masters. Pick a single digit — say, 7 — then scan every row and column that already contains a 7. Those rows and columns create an invisible shadow across the grid, blocking specific cells in each 3×3 box. Where the shadow leaves only one cell unblocked inside a box, that cell must be 7.

The four-step method:

1. Pick a digit. Start with whichever appears most often in the givens — more occurrences mean more blocking constraints.
2. Mark every row and column that already contains that digit.
3. For each box that does not yet contain the digit, the marked rows and columns eliminate candidate cells. Scan what remains in the box.
4. If only one cell in the box is unblocked, fill it in.

Work through all nine boxes for one digit before moving to the next. Cycling through all nine digits — 1 through 9 — constitutes a full cross-hatching pass and typically fills a significant portion of an easy puzzle.

Grid showing all existing 7s (marked with 7; other cells shown as ·):

Col:  1  2  3  4  5  6  7  8  9
     ┌────────┬────────┬────────┐
R1:  │ ·  ·  · │ ·  7  · │ ·  ·  · │  ← row 1 blocked
R2:  │ ·  ·  · │ ·  ·  · │ ·  ·  7 │  ← row 2 blocked
R3:  │ ·  ·  · │ ·  ·  · │ ·  ·  · │
     ├────────┼────────┼────────┤
R4:  │ 7  ·  · │ ·  ·  · │ ·  ·  · │  ← row 4 blocked; col 1 blocked
R5:  │ ·  ·  · │ ·  ·  · │ ·  ·  · │
R6:  │ ·  ·  · │ ·  ·  · │ 7  ·  · │  ← row 6 blocked; col 7 blocked
     ├────────┼────────┼────────┤
R7:  │ ·  ·  7 │ ·  ·  · │ ·  ·  · │  ← row 7 blocked; col 3 blocked
R8:  │ ·  ·  · │ ·  ·  · │ ·  7  · │  ← row 8 blocked; col 8 blocked
R9:  │ ·  ·  · │ ·  ·  · │ ·  ·  · │
     └────────┴────────┴────────┘

Focus: bottom-left box (rows 7–9, cols 1–3).
  Rows blocked: row 7 (has 7 at col 3). Rows 8 and 9 are clear.
  Cols blocked: col 1 (has 7 at row 4), col 3 (has 7 at row 7).
  Remaining candidate: row 8 or 9, col 2 only.
  → Further check: if row 9 col 2 sees another 7 in its column or box, row 8 col 2 is forced.

When a row, column, or 3×3 box has eight of its nine cells filled, the empty cell's value is immediate: it is whichever digit from 1–9 is not yet present in that group. No elimination process is needed — just identify the missing number.

This deduction is the fastest move in Sudoku. Train yourself to notice it constantly: any time you fill a cell, glance at the groups it belongs to. One of those groups may now have only one empty slot.

The last-remaining-cell technique applies equally to columns and to 3×3 boxes. On easy puzzles, several groups will reach this state in the first few moves, creating an acceleration effect: each placement makes more last-remaining-cell situations visible.

A naked single occurs when a cell has exactly one possible value after you eliminate every digit already present in its row, column, and 3×3 box. The remaining candidate is the only legal option — logic guarantees it.

How to find naked singles methodically:

1. Pick any empty cell.
2. List every digit that already appears in the same row — those are forbidden.
3. Add every digit in the same column — also forbidden.
4. Add every digit in the same 3×3 box — also forbidden.
5. If the combined forbidden list covers eight different values (1–8 or 1–9 with one gap), the remaining value is the naked single.

Empty cell at row 5, col 5. Check its three groups:

  Row 5:    already contains 1, 3, 4, 6, 7, 8, 9  (missing: 2, 5)
  Col 5:    already contains 2, 3, 4, 6, 7, 8, 9  (missing: 1, 5)
  Box (4-6, 4-6): already contains 1, 2, 3, 6, 7, 8  (missing: 4, 5, 9)

  Forbidden (union of all three): 1, 2, 3, 4, 6, 7, 8, 9
  Only candidate: 5  ← naked single — fill it with confidence.

On easy puzzles, naked singles appear frequently because so many cells are already filled. Mental scanning is often fast enough — you rarely need to write down candidates. The moment eight constraints are visible, fill the cell.

Random scanning wastes time and causes missed moves. Use a consistent system:

1. Cross-hatch one digit through all nine boxes before moving to the next digit.
2. After each digit pass, scan every row, column, and box for last-remaining-cell situations.
3. Re-scan after every placement. Each cell you fill removes a candidate from up to 20 other cells — the row, column, and box it sits in. Check those groups immediately for newly exposed naked singles.
4. Repeat until the puzzle is complete.

Most easy puzzles yield fully after one or two complete passes. If you finish a pass and find no new moves, double-check your constraint application — you have almost certainly missed a naked single somewhere. Slow down and check each empty cell deliberately.

On easy difficulty you rarely need pencil marks — the clue density makes most naked singles visible at a glance. However, two situations benefit from them:

• When you feel stuck: If no move is apparent, write the candidates for a complete row or box. You will often spot a naked single immediately — it was there the whole time, just not obvious without the explicit list.
• Learning the process: If Sudoku is new to you, filling in all candidates for one 3×3 box is an excellent practice exercise. Seeing which digits get eliminated by which constraints builds the pattern recognition that later becomes intuitive.

In Sudoku Rise, tap the pencil icon or press N (desktop) to switch to notes mode. Tapping a digit writes or removes that candidate in the selected cell. Candidates update automatically when you place a digit elsewhere in the same group.

Skipping the box constraint. New players scan rows and columns instinctively but forget that the 3×3 box is an equally hard constraint. Always check all three groups. A digit may be free in a row and column but already present in the box — or vice versa.

Filling in pencilled candidates as confirmed. A pencil mark means "possible", not "certain". Only commit a value when logic narrows the candidates to exactly one.

Guessing. Easy puzzles never require guessing. If you feel uncertain, look again — you have missed a logical constraint. Guessing one wrong cell can cascade into a dozen wrong cells before you notice the contradiction. Use the undo button instead.

Skipping re-scans after placements. Every number you enter eliminates candidates from its entire row, column, and box. Never move on without checking those groups for new naked singles or last-remaining-cell situations.

Going too fast. One wrong placement early in the puzzle forces errors throughout. Accuracy beats speed, especially while building fluency.

Solve easy puzzles daily until the cross-hatching and naked-single patterns feel automatic — your eye should spot them without deliberate effort. A reasonable benchmark: under 10 minutes per easy puzzle with zero errors. When you consistently hit that mark, you are ready for medium difficulty.

The three techniques covered here — cross-hatching, last remaining cell, naked singles — never become obsolete. They remain the starting point on every medium, hard, and expert puzzle. Master them completely before moving on.