Kode strategy guide
Every Kode board is built to be solved with logic alone. You never need to guess, but you do need to know where to look. The seven techniques below are all it takes, and they are the same moves the solver uses to check each puzzle before it is published. They come in two stages: first work out which four digits are in the code, then work out where each one goes.
The example board
Every example in this guide uses the same five clues, taken from Kode #100 in the archive. Keep them in view as you read. ▲ counts digits in the right spot; ● counts digits that are in the code but in the wrong spot.
Stage 1: find the four digits
The code uses four different digits out of ten. Your first job is to sort all ten into "in" and "out". Ignore positions for now: it's much easier to place digits once you know which ones you're placing.
1. Start with the blank row
Look for a row with no marks at all, ▲0 ●0. It is the most generous clue on the board: none of its four digits is in the code, so four of the ten digits disappear at once. Almost every board has one, and it is nearly always the best first move.
Row 5 (7 9 8 1) has no marks. Cross out 7, 9, 8 and 1. Six digits remain: 0, 2, 3, 4, 5 and 6.
2. Fill a row when the count matches
Add a row's marks together, ▲ plus ●, to get how many of its digits are in the code. Then set aside the digits you already know are out. If the number of undecided digits left equals the number of marks still unexplained, every one of them must be in.
Row 1 (7 6 3 8) has two marks. 7 and 8 are already out, so both marks belong to 6 and 3: both are in the code. The same move on row 3 (4 7 9 8) finds 4, since 7, 9 and 8 are out and the row still has one mark.
3. Empty a row when its marks are used up
The same arithmetic works in reverse. If a row's marks are already explained by digits you know are in the code, there is nothing left for the other digits in that row. They are all out.
Row 2 (7 9 3 0) has one mark, and we already know 3 is in. That mark is 3's, so 0 is out.
4. Close the set
As soon as you have four digits in, the other six are out. And if six digits are out, the remaining four must be the code's digits. Either way, membership is settled, and every row on the board becomes easier to read.
Row 4 (2 9 1 4) has two marks. 9 and 1 are out and 4 is in, which leaves one mark for 2, so 2 is in. That makes four: 2, 3, 4 and 6. The last undecided digit, 5, is out.
Stage 2: put them in order
With the four digits known, the question becomes where each one sits. The ▲ marks now do the heavy lifting, together with one simple rule: four digits, four positions, no repeats.
5. A row with no ▲ shows four wrong places
If a row has no ▲, none of its digits is where that row shows it. Each such row hands you up to four "not here" facts for free. The same goes for any row whose ▲ is already accounted for: once you have placed the digit that earns its ▲, the row's other in-code digits are all in the wrong spot.
Row 2 (7 9 3 0) has no ▲ and shows 3 in position 3, so 3 is not in position 3. Likewise, row 3 puts 4 in position 1 and row 4 puts it in position 4, both with no ▲, so 4 is in neither of those spots.
6. Count the ▲
When every digit in a row is decided, look only at its in-code digits. The ▲ number says how many of them sit exactly where the row shows them. If just that many of them could still be in place, because the others are ruled out, those digits are locked in.
Row 1 (7 6 3 8) has one ▲, and its in-code digits are 6 in position 2 and 3 in position 3. Row 2 rules out 3 in position 3, so the ▲ must be the 6. The 6 goes in position 2.
7. Last spot standing
Now check each digit and each position in turn. A digit with only one position left goes there; a position with only one possible digit takes it. Each placement removes options for the others, so the last few digits tend to fall in quick succession.
4 can't be in position 1 (row 3) or position 4 (row 4), and position 2 already holds 6, so 4 goes in position 3. Row 4 also shows 2 in position 1 with no ▲, which leaves 2 only position 4. The 3 takes the last gap, position 1. The code is 3642.
Common mistakes
- Reading ● as "wrong digit"
- An amber ● means the digit is in the code, just not in that spot. Only a row's missing marks tell you a digit is out. Mixing the two up is the quickest way to throw away a correct digit.
- Assuming the marks point at particular digits
- A row's ▲ and ● are counts for the whole row, not labels on individual tiles. ▲1 does not mean the first digit is right; it means one of the four, somewhere, is. You find out which by comparing rows.
- Leaving a row once its digits are sorted
- A row whose digits are all known to be in or out still has its ▲ count to give. Some of the most useful placements come from rows you thought you had finished with.
Good habits
- Mark as you go
- In the game, tap any clue tile to pencil-mark it red, yellow or green, and long-press to clear it. The marks never affect the grading, but keeping track of what is out and what is placed stops you from working out the same fact twice.
- Test your answer against every row
- You have three tries. Before entering a code, check it against each clue: count how many of its digits would be ▲ and how many ●, and make sure every row matches. If one disagrees, you have slipped somewhere, and you have just saved a try.
- Practise on the archive
- Every past puzzle has spoiler-free hints and a step-by-step solution. Try a board cold, then open the solution and compare your route with the solver's. Over time you will start to spot the blank row and the decisive ▲ at a glance.