Kefiw

Archived noindex page. Kefiw's public focus is Property decision help.

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This older Kefiw page is kept for reference, marked noindex, and removed from the primary sitemap. The current Kefiw experience is focused on property decisions: cost, quotes, damage, buying, selling, owning, and packets.

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Sudoku Difficulty Levels Explained

Each difficulty is defined by the techniques it requires — not just fewer clues.

Match the techniques to the level — easy wants scanning, expert wants chains — and your solve times stabilise at every tier.

Difficulty in Sudoku is not really about how many starting clues you get — it is about which logical techniques you need to finish. Easy puzzles surrender to a single scan for naked and hidden singles. Expert puzzles resist every basic move and require colouring chains or nice loops. Kefiw runs four tiers (~36, ~30, ~26, ~22 clues) that map cleanly to four technique tiers.

Part of: Daily Challenges

Quick answer

Match the techniques to the level — easy wants scanning, expert wants chains — and your solve times stabilise at every tier.

What you are trying to do
Each difficulty is defined by the techniques it requires — not just fewer clues.
Best next step
Sudoku
Limit to remember
Treat this as a practical aid for the task, not a replacement for professional judgment.

Key points

  • ▸ Easy (~36 clues): naked singles and hidden singles are enough. Typical solve 3–7 minutes.
  • ▸ Medium (~30 clues): add locked candidates (pointing pairs and claiming pairs) — a digit in a box that can only sit in one row cleans that digit from the rest of the row. Typical solve 7–15 minutes.
  • ▸ Hard (~26 clues): naked and hidden pairs/triples, then X-Wing and basic Swordfish patterns. Typical solve 15–30 minutes.
  • ▸ Expert (~22 clues): colouring chains, XY-Wing, Swordfish, uniqueness rectangles, and simple nice loops. Below 20 clues the puzzle often has no forcing chain-free path. Typical solve 30+ minutes.
  • ▸ The theoretical minimum for a uniquely-solvable Sudoku is 17 clues, proven by exhaustive search in 2012 — most expert puzzles stay at 22–24 to remain human-solvable.
  • ▸ Climb a tier only when the current tier solves reliably without guessing in under the lower solve-time band — jumping early builds the guess-and-check habit, which caps growth.

Examples

  • Easy puzzle, naked single
    A cell with 1, 2, 3, 4, 5, 6, 7, 8 already present in its row, column, or box — 9 is the only candidate. Fill, move on. Easy boards surrender entirely to this scan.
  • Medium, pointing pair
    Box 1 has the digit 3 only available in r1c2 and r1c3. Therefore 3 cannot appear elsewhere in row 1 — eliminate the candidate from r1c4 through r1c9. Medium puzzles hinge on moves like this one.
  • Hard, X-Wing
    Digit 7 appears as a candidate in exactly two columns of rows 2 and 6, forming a rectangle. That means 7 must go in two diagonal corners of the rectangle — eliminate 7 from every other cell in those two columns.
  • Expert, XY-Wing
    Three cells hold candidate pairs (AB), (BC), (AC) with the pivot seeing both wings. Any cell seeing both wings cannot hold A — the elimination unlocks the chain. Expert boards often have one or two of these as the only path forward.

When to use which tool

▸ Operational Thresholds
  • CYAN · STABLE — Solve time sits in the lower half of the band for your tier — plateau is stable, consider climbing a level.
  • GOLD · GUARDED — Solve time hovers near the upper edge of your tier band — plateau is guarded, stay at this tier one to two more weeks.
  • MAGENTA · CRITICAL — Solve time exceeds the band by 50% or you are guessing to finish — plateau is critical, drop one tier and rebuild the technique base.
▸ Pivot
Pick a tier and start — each difficulty keeps its own saved board, so you can work several in parallel.
Sudoku →

Related

Frequently asked questions

› Why does clue count not fully determine difficulty? Troubleshooting

Two puzzles with 26 clues can be wildly different — one may fall to singles and pairs, another may require Swordfish. The generator enforces a difficulty class by the hardest technique needed, not raw clue count.

› Is every uniquely-solvable puzzle logic-solvable without guessing? Trust & accuracy

Yes in theory — if the solution is unique, a sufficiently powerful technique set finds it. In practice, some "evil" puzzles require chains long enough that guess-and-check is faster for humans.

› Should I keep climbing difficulty or plateau on one level? Trust & accuracy

Plateau first. The working-memory and scanning reflex need weeks of repetition at a stable tier before they transfer to the next. Climbing too fast caps growth around medium forever.

› How do I use a puzzle helper without spoiling the game? How-to

Use a puzzle helper after your own first attempt, not before every move or answer. Read the rules, try a round cold, then use the guide to understand misses, patterns, and better strategy. That keeps the puzzle fun while turning mistakes into practice.

› What should I learn first in a new puzzle game? Definition

Learn the rules, win condition, scoring, and one opening habit before chasing advanced tactics. Most players improve fastest by removing obvious mistakes: unclear turns, wasted guesses, ignored constraints, or overusing hints. Strategy only matters once the basic loop is automatic.