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QuasigroupCompletion.java
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QuasigroupCompletion.java
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// Copyright 2011 Hakan Kjellerstrand [email protected]
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.ortools.contrib;
import com.google.ortools.constraintsolver.*;
import com.google.ortools.constraintsolver.DecisionBuilder;
import com.google.ortools.constraintsolver.IntVar;
import com.google.ortools.constraintsolver.Solver;
import java.io.*;
import java.text.*;
import java.util.*;
public class QuasigroupCompletion {
static {
System.loadLibrary("jniortools");
}
static int X = 0;
/*
* default problem
*
* Example from Ruben Martins and Ines Lynce
* Breaking Local Symmetries in Quasigroup Completion Problems, page 3
* The solution is unique:
*
* 1 3 2 5 4
* 2 5 4 1 3
* 4 1 3 2 5
* 5 4 1 3 2
* 3 2 5 4 1
*/
static int default_n = 5;
static int[][] default_problem = {
{1, X, X, X, 4},
{X, 5, X, X, X},
{4, X, X, 2, X},
{X, 4, X, X, X},
{X, X, 5, X, 1}
};
// for the actual problem
static int n;
static int[][] problem;
/**
* Solves the Quasigroup Completion problem. See
* http://www.hakank.org/google_or_tools/quasigroup_completion.py
*/
private static void solve() {
Solver solver = new Solver("QuasigroupCompletion");
//
// data
//
System.out.println("Problem:");
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
System.out.print(problem[i][j] + " ");
}
System.out.println();
}
System.out.println();
//
// Variables
//
IntVar[][] x = new IntVar[n][n];
IntVar[] x_flat = new IntVar[n * n]; // for branching
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
x[i][j] = solver.makeIntVar(1, n, "x[" + i + "," + j + "]");
x_flat[i * n + j] = x[i][j];
}
}
//
// Constraints
//
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (problem[i][j] > X) {
solver.addConstraint(solver.makeEquality(x[i][j], problem[i][j]));
}
}
}
//
// rows and columns must be different
//
// rows
for (int i = 0; i < n; i++) {
IntVar[] row = new IntVar[n];
for (int j = 0; j < n; j++) {
row[j] = x[i][j];
}
solver.addConstraint(solver.makeAllDifferent(row));
}
// columns
for (int j = 0; j < n; j++) {
IntVar[] col = new IntVar[n];
for (int i = 0; i < n; i++) {
col[i] = x[i][j];
}
solver.addConstraint(solver.makeAllDifferent(col));
}
//
// Search
//
DecisionBuilder db = solver.makePhase(x_flat, solver.INT_VAR_SIMPLE, solver.ASSIGN_MIN_VALUE);
solver.newSearch(db);
int sol = 0;
while (solver.nextSolution()) {
sol++;
System.out.println("Solution #" + sol + ":");
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
System.out.print(x[i][j].value() + " ");
}
System.out.println();
}
System.out.println();
}
solver.endSearch();
// Statistics
System.out.println();
System.out.println("Solutions: " + solver.solutions());
System.out.println("Failures: " + solver.failures());
System.out.println("Branches: " + solver.branches());
System.out.println("Wall time: " + solver.wallTime() + "ms");
}
/**
* Reads a Quasigroup completion file. File format: # a comment which is ignored % a comment which
* also is ignored number of rows (n) < row number of space separated entries >
*
* <p>"." or "0" means unknown, integer 1..n means known value
*
* <p>Example 5 1 . . . 4 . 5 . . . 4 . . 2 . . 4 . . . . . 5 . 1
*/
private static void readFile(String file) {
System.out.println("readFile(" + file + ")");
int lineCount = 0;
try {
BufferedReader inr = new BufferedReader(new FileReader(file));
String str;
while ((str = inr.readLine()) != null && str.length() > 0) {
str = str.trim();
// ignore comments
if (str.startsWith("#") || str.startsWith("%")) {
continue;
}
System.out.println(str);
if (lineCount == 0) {
n = Integer.parseInt(str); // number of rows
problem = new int[n][n];
} else {
// the problem matrix
String row[] = str.split(" ");
for (int i = 0; i < n; i++) {
String s = row[i];
if (s.equals(".")) {
problem[lineCount - 1][i] = 0;
} else {
problem[lineCount - 1][i] = Integer.parseInt(s);
}
}
}
lineCount++;
} // end while
inr.close();
} catch (IOException e) {
System.out.println(e);
}
} // end readFile
public static void main(String[] args) throws Exception {
if (args.length > 0) {
String file = "";
file = args[0];
QuasigroupCompletion.readFile(file);
} else {
problem = default_problem;
n = default_n;
}
QuasigroupCompletion.solve();
}
}