What kind of puzzle is Kakuro?
Kakuro is a number puzzle where the small clue in each black cell tells you the sum of the white cells running to its right or downward, and you fill those cells with digits from 1 to 9. Think of a crossword where numbers take the place of words, which is why it is also called cross sums or a number crossword.
Each black clue cell is split by a diagonal. The upper right number is the sum of the white cells to the right of it, and the lower left number is the sum of the white cells below it. Every white cell belongs to one across run and one down run at the same time, so the digit you place has to satisfy both sums. Those are the only two rules, yet narrowing down the combinations feels quite different from sudoku.
| Rule | Detail |
|---|---|
| Digits | Only 1 to 9 go into white cells. There is no 0. |
| Sums | The clue in a black cell equals the sum of the white cells in that direction |
| No repeats | Within one run (a group of white cells between black cells) each digit may appear once |
| Other runs | Different runs may share digits. There is no whole board constraint like sudoku. |
| Solution | Every board is built to have exactly one answer, so it can be solved by logic alone. |
Where do I start solving?
Look for runs with only one possible combination. A two cell run summing to 3 must be 1 and 2; summing to 17 it must be 8 and 9. A three cell run summing to 6 is 1, 2, 3 and summing to 24 is 7, 8, 9. Four cells summing to 10 or 30 and five cells summing to 15 or 35 are fixed too.
Where two such runs cross, only a digit common to both combinations can go in the shared cell, so it is settled at once. A two cell 4 (1, 3) crossing a three cell 7 (1, 2, 4) gives a 1 in the crossing cell. When you select a cell, the helper line below the board shows the remaining sum and the possible combinations of both its runs, so at first you can fill cells one at a time just by reading it.
| Cells | Sums with a single combination |
|---|---|
| 2 | 3 = 1+2 · 4 = 1+3 · 16 = 7+9 · 17 = 8+9 |
| 3 | 6 = 1+2+3 · 7 = 1+2+4 · 23 = 6+8+9 · 24 = 7+8+9 |
| 4 | 10 = 1+2+3+4 · 11 = 1+2+3+5 · 29 = 5+7+8+9 · 30 = 6+7+8+9 |
| 5 | 15 = 1+2+3+4+5 · 16 = 1+2+3+4+6 · 34 = 4+6+7+8+9 · 35 = 5+6+7+8+9 |
How do the difficulty levels differ?
By board size. Easy is 6×6, Normal is 8×8 and Hard is 10×10. Larger boards have longer runs and more sums with many combinations, and Hard includes five cell runs.
Every board is generated fresh. The layout starts from a diagonal staircase pattern and is shuffled at random, the white cells are filled with digits, and a solver checks that the answer is unique. If another answer exists, the digits that allow it are changed until only one answer remains. So no two boards are alike, and each one can be finished by logic from start to end.
What is the daily puzzle?
The daily button on the title screen uses a seed made from the date, so everyone gets the same Normal 8×8 board that day. It changes at midnight Korea time.
When you finish, your time is recorded and shown on the daily button, and Share result makes a card you can send to friends to compare times. The link on the card carries the board number, so the same board opens for them.
How do memo, hint and undo work?
- Memo: turn Memo on and tap digits to pencil candidates into the corner of a cell. When you place a final digit, that digit is removed from the memos in the same runs.
- Hint: if the selected cell is empty or wrong, its answer is filled in; otherwise the empty cell with the fewest candidates is filled. Hinted digits are shown in brown and the hint count appears in your result.
- Undo: steps back one entry at a time, up to 400 moves.
- Wrong sums: when a run is full but its sum is off, a digit is repeated, or the remaining cells can no longer reach the sum, the clue and the digits of that run turn red.
Tips for solving Kakuro faster
- Mark the single combination runs first. Two cell sums of 3, 4, 16, 17 and three cell sums of 6, 7, 23, 24 have fixed digits.
- Watch the crossings. Only a digit in both the across and the down combination can sit in a shared cell. One common digit means it is settled.
- Think of long runs by what is missing. A four cell 29 is 5, 7, 8, 9, so for big sums it is quicker to find the one small digit that is left out.
- Follow the remaining sum. The helper line shows what is left in each run. Every settled cell shrinks the combinations of its neighbours.
- Use memos when stuck. Pencil the two candidates of a cell and you will notice the moment another run removes one of them.
Controls
- Phone and tablet: tap a cell, then a digit button below. Tapping the same digit again clears it. Memo, hint, undo and erase are on the buttons below the digits.
- Keyboard: 1 to 9 to enter, arrow keys to move, Backspace, Delete or 0 to clear, N to toggle memo, H for a hint, Z or U to undo.
- Layout: in landscape the digit pad sits on the right as a 3×3 grid; in portrait it sits below the board in one row.
An unfinished board is saved in this browser and comes back through Continue on the title screen. Best times per level stay in the same browser and are never sent to a server.