JCO Website (Puzzles for the manual solver)

Welcome!

This is a place chosen to make available some ideas (on puzzles, patterns, etc)

that seemed unsuitable for posting in a Forum, but some people may find interesting.

For difficult puzzles, possible solutions will not be shown (only hints).

For other puzzles, the solution wil be hidden so that a serious attempt can be made

without direct access to a solution.

(hopefully this will make the puzzles more interesting for newcomers)

(Guidelines for using this site here)

Links for Basic Concepts

(useful to look up for the meaning of some unfamiliar concept)

• Sudopedia
• HoDoKu
• Hashi

Rules

• Slitherlink
• Hidoku
• Hashi

Recent Puzzles (*1*)

Puzzle LS#7 (overall #140) (6x6 Latin Squares; proposed Oct 12, 2026)

I propose the following tough 6x6 Latin Squares Puzzle (SE = 8.3).

(generated with SudokuExplainer)

Initial grid

  +-------------+
6 | . 1 . . . . |
5 | 5 4 . . . . |
4 | . . 2 1 . . |
3 | . . 5 2 3 1 |
2 | . . . 5 . . |
2 | . . . 3 . 4 |
  +-------------+ Latin Squares
    a b c d e f
    

Recent Problems (*1*)

Problem #8: Chess (Proposed Oct 11, 2026)

Consider the chess position above. Black played 10... Qxa1.

What should be white's response ? How the game should continue with correct play ?

Initial position (and last move played):

White: Ke1, Bc1, Bf1, Rh1, Ng6, Qh5, a2, b2, c4, d2, e3, g2, h2.
Black: Ke8, Qa1, Ra8, Rh8, Nb8, Ng8, Bc8, Bf8, a7, b7, c7, f6, h7.

(Black's last move: 10... Qxa1)

Past Puzzles (*139*)

• Past proposed 9x9 CLASSIC SUDOKU PUZZLES (55) are HERE
• Past proposed SLITHERLINK PUZZLES (31) are HERE
• Past proposed 9x9 JIGSAW SUDOKU PUZZLES (6) are HERE
• Past proposed 6x6 SUDOKU-X PUZZLES (16) are HERE
• Past proposed 9x9 SUDOKU-X PUZZLES (2) are HERE
• Past proposed LATIN SQUARES PUZZLES (6) are HERE
• Past proposed HIDOKU PUZZLES (15) are HERE
• Past proposed 6x6 CLASSIC SUDOKU PUZZLES (7) are HERE
• Past proposed HASHI PUZZLES (1) are HERE

Past Problems (*7*)

Interesting Forums ( in particular, very fond of the NSPF! )

• Sudoku (The New Sudoku Player's Forum - NSPF)
• Puzzles
• Solving without Pencilmarks by RW
• How to find ALSs to build a chain by JCO
• Hard 5x5 Latin Squares by qiuyanzhe
• Hardest 6x6 ? by 999_Springs
• hardest 6x6 sudoku-x ? by 1to9only
• AIC by Myth Jellies
• Sudoku Online (AU)
• Puzzling (StackExchange)

Created: February 12, 2024

Contact: sudo.jco.br@gmail.com