# SCIP

Solving Constraint Integer Programs

Sudoku Solver

# Methodology

To solve the given sudoku puzzle using integer programming, we shall use this handy tutorial; http://profs.sci.univr.it/~rrizzi/classes/PLS2015/sudoku/doc/497_Olszowy_Wiktor_Sudoku.pdf

An unsolved sudoku puzzle looks like below:
 +-------—+--------—+--------—+ |* * * | * * * | * * * | |* 3 * | * 1 2 | * * 8 | |* 7 * | * 6 8 | * 2 * | +-------—+--------—+--------—+ |* * * | * * 9 | 8 7 * | |1 2 * | 6 5 * | 4 * * | |* * * | * * * | * * 6 | +-------—+--------—+--------—+ |* * 3 | 9 4 * | * * * | |* * * | 2 * * | * 6 * | |4 * * | * * * | * 3 1 | +-------—+--------—+--------—+ 

The solved puzzle will have each of the nine rows and columns filled by numbers 1, ..., 9 each appearing exactly once. There are 9 subgrids and each subgrid also needs to be filled by numbers 1, ..., 9 each appearing exactly once. As seen in the unsolved puzzles, some of the positions are already filled.

In this example, we see

• how to model problems with many variables in SCIP,
• how to set parameters
• how use the solution status to print custom output messages.

# Data Format

A sudoku puzzle is in represented by a string of 81 charcaters. An already filled number in the puzzle is represented by that number; a blank is represented by either '.' or '0' in the puzzle string. The input file is containing the configuration of a sudoku read rowwise as a string. For example, the above puzzle is represented by 000000000030012008070068020000009870120650400000000006003940000000200060400000031 or ..........3..12..8.7..68.2......987.12.65.4..........6..394.......2...6.4......31

# Installation

See the Install file