Getting Started

Strategies Overview

Simple puzzles can be solved by looking for cells where only one number is allowed, or looking for numbers where only one cell in a group is allowed. Examples of these strategies are:

• Only one cell is not solved in a group
• Basic Intersecting groups: only one number is possible where they intersect
• Linked Intersecting groups: intersections with one group place limitations on intersections with other groups that lead to only one number being possible in the latter intersection.

More complex puzzles require noting in empty cells which numbers are possible and which are impossible, then detecting patterns that lead to another cell solved. Although these strategies can be employed "in your head", they are much easier when impossibles are marked. Examples of these strategies are:

• Solve a cell with only one number possible (all other numbers have been marked impossible)
• Solve the only cell in a group where one number is possible (that number is impossible in all other cells in the group)

The following strategies do not directly solve a cell, but mark numbers impossible in cells, hopefully leading to a solution by one of the simpler strategies

• Find Box Eliminations looks for situations where a number must be in a row or column of a box, therefore that number cannot be in any other rows/columns of that box and should be marked impossible there.
• Find N-tuplets (an N-tuplet is a couplet, triplet, quadruplet, etc.) looks for N cells in a group that contain exactly N different numbers. Since those N numbers must be in those N cells, those numbers are marked impossible in all other cells of that group.
• Find Hidden N-tuplets looks for N different numbers that are found in exactly N different cells in a group. Since those N cells must contain those N numbers, all other numbers in those cells are marked impossible.

Some puzzles cannot be solved with the above strategies. At this point the user must save the puzzle, then make a guess. This is referred to as the Pick a trial number strategy. If the guess leads to a conflict, then the user must reload the saved puzzle and make a different guess. Usually one correct guess is sufficient to solve the puzzle, but occasionally the Pick a trial number strategy must be employed several times.

Note that a given cell could often be solved by any of several strategies.

Next: Using the Zudoku Program