SudokuWiki.org
Strategies for Popular Number Puzzles

#709, August 1 - August 7, 2026:
The Weekly 'Unsolvable' Sudoku Puzzle

by Richard Kröger, guest compiler

WARNING: This is the Weekly 'Unsolvable' Sudoku, rated above 'Extreme'.
This is currently unsolvable by my solver, except perhaps with trial and error strategies.
Using the solver will not help you. (much).

Changes March 2026

Due to the introduction of Forcing Nets many Weekly Unsolvable puzzles can now be solved. I have flagged all the Sudoku ones which are solvable. I am struggling to make any new ones so we'll have to see if the Weekly can continue. The point of the Weekly was to provoke discussion and new ideas, so that is progress. But my solution is unlikely to be optimal so alternatives are welcome.

Archive

Each week a new 'unsolvable' will be published and the previous will be accessible here from this archive section. If you like very tough puzzles, these are for you.
Share and Enjoy
Supporter Members have access to all these puzzles going back to number 1.

Discussion...

Post an idea here...
Your Name or Handle

Your suggestion, idea or question

Please enter the
letters you see:
arrow
Enter these letters



Please keep your comments relevant to this puzzle.
Email addresses are never displayed, but they are required to confirm your comments. To state your solve time use the smaller form at the top right of this page. Line breaks and paragraphs are automatically converted ? no need to use <p> or <br> tags.

Saturday 1-Aug-2026

... by: Norman Powell

Unsolvable with deterministic methods, one use of Bowman's Bingo solves. I get many more eliminations using Forcing Network first.
X-Cycles: Eliminate 3 from H6 since it can see both ends of a chain.
Forcing Networks 1st Pass:
Eliminate 4 from B5, 1 from C4, 4 from C4, 4 from C6, 5 from E5, 1 from H1.
Forcing Networks 2nd Pass:
Eliminate 1 from A9, 9 from B6, 1 from C6, 1 from D5, 5 from H6, 5 from J6
Forcing Networks 3rd Pass:
Eliminate 2 from A7, 5 from H4
Forcing Networks 4th Pass:
Eliminate 2 from E9, 2 from H9, 2 from J9
Bowman's Bingo: Eliminate 2 from A3 after 20 trials over 6 Levels of trial guesses.
Solved A3 as 7
Hidden Singles: Row A, A9=2, Row E, E5=7, Row F, F1=7
WXYZ-Wing: Hinge E9, Corners E3, B9, D9 Constrained Values 3, 9, 6
Eliminated Unconstrained Value 5 from Cell E7
Solved E8 = 2
Hidden Single Row D, D6=2
Confined to Box: Value 1 is confined to Row D and Box 4, Eliminate 1's from elsewhere in Row D or Box 4.
Subset Exclusion: Pair H9 & J9 - Pair of Cells can see value 5
Locked Set Cells B9, D9, E9 excludes Values 9
Locked Set Cells H8, G8 excludes Value 1
Eliminate 5 from H9
Confined to Box: 5 is confined to Row H and Box 9 Eliminate from other areas of Row H and Box 9.
Hidden Triplets in Row J for Values 5, 6, 8 in Cells J2, J4 and J5, eliminate other values in those Cells.
WXYZ-Wing Hinge F4 Corners F6, C4, J4 constrained Values 1 8 6
Eliminate unconstrained value 5 from Cell E4.
Solved Cell: E4 = 4
WXYZ-Wing Hinge D9 Corners D5, D7 B9 Constrained Values 5 6 8
Eliminate 3 from E9
WXYZ-Wing Hinge F7 Corners F4, C4, J4 Constrained Values 8 9 1
Eliminate 5 from F8
Hidden Singles: Column 8 H8 = 5, Column 1 H1 = 3, Row E, E2 = 3
Confined to Box:
9 is confined to Column 3 and Box 4, eliminate other 9's in Column 3 or Box 4
4 is confined to Row G and Box 9, eliminate other 4's in Row G or Box 9
Rectangular Elimination 9 On in Cell G5 and Strong ling B5 and B1 would eliminate all the 9's from Box 7 so eliminate.
XY-Cycle: 1 in F4 can see both ends of chain, so eliminate.
Hidden Singles: Box 2, B5 = 9, Column 6, C6 = 5, Row F F6 = 1
Solved Cell: C4 = 6
Hidden pair in Box 6 for values 5 9 in Cells E9 F7, eliminate other values in those cells
Hidden pair in Column 9 for values 3 6 in cells B9 and D9, eliminate other values in those cells.
Solved Cells: F7 = 9, E9 = 5, D3 =9
Naked Pair in Column 4 for Values 5 & 8 in Cells F4 and J4, eliminate values 5 & 8 from other cells in Column 4.
X-Cycle: Value 8 in F7 has weak links to both ends of chain eliminate.
16 Solved Cells and Hidden Singles
Y-Wing: Hinge H3, Corners D3 and J2 Constrained Values 1 & 8
Eliminate unconstrained Value 6 from cells D2 and G3.
The remainder Solved Cells and Hidden Singles

Saturday 1-Aug-2026

... by: Dieter

#709 - initially populated cells: 23 = 28,4 %
No solver used, solver = brain.

Strategy: numbers 3,5,6,7,8 occur most frequently, combine two cells with almost same candidates.
combinations of D7 = (2,3,8) and D9 = (2,3,5,6)
after basic checks 4 matrices left: 3/5, 3/6, 8/3 and 8/5
D7=8 & D9=3 solve with J2=6.

Optimization:
D9=3 & J2=6 solve.

Saturday 1-Aug-2026

... by: Serban

# 709 Basics to 23

1. D9=3 & G5=6 solve

2. D9=3 & J5=8 solve

3. J6=9 & J5=8 solve
Page created on 03-May-2011, last modified on 30-May-2024.
All puzzles on this site are trademarked and copyright
and cannot be reproduced without permission.
Copyright Andrew Stuart @ Syndicated Puzzles, Privacy, 2007-2026