/** Solves the Coins Grid problm. See http://www.hakank.org/google_or_tools/coins_grid.py */
private static void solve() {
Solver solver = new Solver("CoinsGrid");
//
// data
//
int n = 31;
int c = 14;
//
// variables
//
IntVar[][] x = new IntVar[n][n];
IntVar[] x_flat = new IntVar[n * n];
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
x[i][j] = solver.makeIntVar(0, 1, "x[" + i + "," + j + "]");
x_flat[i * n + j] = x[i][j];
}
}
//
// constraints
//
// sum row/columns == c
for (int i = 0; i < n; i++) {
IntVar[] row = new IntVar[n];
IntVar[] col = new IntVar[n];
for (int j = 0; j < n; j++) {
row[j] = x[i][j];
col[j] = x[j][i];
}
solver.addConstraint(solver.makeSumEquality(row, c));
solver.addConstraint(solver.makeSumEquality(col, c));
}
System.out.println("here1");
// quadratic horizonal distance
IntVar[] obj_tmp = new IntVar[n * n];
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
obj_tmp[i * n + j] = solver.makeProd(x[i][j], (i - j) * (i - j)).Var();
}
}
IntVar obj_var = solver.makeSum(obj_tmp).Var();
//
// objective
//
OptimizeVar obj = solver.makeMinimize(obj_var, 1);
//
// search
//
DecisionBuilder db =
solver.makePhase(x_flat, solver.CHOOSE_FIRST_UNBOUND, solver.ASSIGN_MAX_VALUE);
solver.newSearch(db, obj);
//
// output
//
while (solver.nextSolution()) {
System.out.println("obj_var: " + obj_var.value());
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.wall_time() + "ms");
}