The goal of Sudoku

Fill every empty square in the 9 × 9 grid with a number from 1 through 9. Each row, each column, and each bold 3 × 3 box must contain all nine numbers exactly once.

The starting numbers are clues and cannot be changed. A well-made puzzle has one solution, and you can reach it with logic rather than arithmetic. The numbers are symbols here: you never need to add, subtract, or calculate.

Rows, columns, and boxes

Every empty square belongs to one row, one column, and one box at the same time. A number is legal only when it does not already appear in any of those three groups.

  • A row runs horizontally across nine squares.
  • A column runs vertically through nine squares.
  • A box is one of the nine bold 3 × 3 regions.

Make your first move

Start with a row, column, or box that is nearly full. List the numbers from 1 to 9 that are missing, then check the crossing row and column for each empty square. If only one missing number can fit a square, you have a certain move.

After placing a number, scan the same row, column, and box again. One answer often removes a candidate from nearby squares and reveals the next answer.

Use notes for candidates

When a square has two or three possible numbers, add small candidate notes instead of guessing. Keep a note only while that number remains legal in the square’s row, column, and box.

The game’s Notes button switches the number pad into candidate mode. When you place a final answer, matching notes are removed from its row, column, and box automatically.

How to spot a conflict

Repeating a number in a row, column, or box breaks the Sudoku rules. The game highlights conflicts so you can compare the affected squares.

A wrong answer does not end the game. Erase the square, reconsider its candidates, and continue. If you are completely stuck, select an empty square and use Hint to reveal it.

A simple solving routine

  • Scan the fullest rows, columns, and boxes first.
  • Place numbers only when you can explain why they fit.
  • Add notes when more than one candidate remains.
  • After every answer, rescan the three groups it touches.
  • Move to another part of the board when one area stops producing certain moves.