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Kode #23: hints & solution

Here's the clue board for Kode #23. Start with the spoiler-free hints. If you're still stuck, the full step-by-step solution is below, hidden until you open it.

The clue board

Each row is a guess that's already been graded. ▲ means a right digit in the right spot; ● means a right digit in the wrong spot.

  • 18903▲1●1
  • 28974▲0●1
  • 37693▲0●1
  • 41957▲0●0
  • 54257▲0●2

Spoiler-free hints

  • 3 of the four digits are even.
  • The four digits add up to 9.
  • Every digit is below 5.

Try the hints first. The solution below walks through every deduction.

Step-by-step solution

Every Kode can be cracked by pure deduction, with no guessing. This board falls in 9 logical steps. Open the solution to follow them one at a time.

Show the solution · reveals the code

When a row "rules out" a position, it shows that digit there but its ▲ marks are already used up (or it has none), so the digit can't sit there.

  1. Row 4 (1 9 5 7) has no marks at all, so 1, 9, 5, and 7 are not in the code.
  2. Row 5 (4 2 5 7) has 2 marks still unexplained, and only 2 digits are left undecided: 4 and 2. So both are in the code.
  3. Row 2 (8 9 7 4) has one mark, already accounted for by 4. That rules out 8.
  4. Row 1 (8 9 0 3) has 2 marks still unexplained, and only 2 digits are left undecided: 0 and 3. So both are in the code.
  5. Row 3 (7 6 9 3) has one mark, already accounted for by 3. That rules out 6.
  6. Row 1 (8 9 0 3) has one digit in the right spot. Since row 3 rules out the 3 in position 4, it has to be the 0 in position 3.
  7. The 4 has only one spot left: position 2 (row 5 rules out position 1, row 2 rules out position 4, and position 3 is already 0).
  8. The 3 has only one spot left: position 1 (row 3 rules out position 4, position 2 is already 4, and position 3 is already 0).
  9. That leaves the 2 for position 4.

That cracks it: the code is 3402.

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