sum one variable (X[i][j]) in one constraint with choco - choco

Question

I am using choco to solve a CSP , and one of my constraints is that the sum of one variables (X[i][j]) is less than N=10, and i=j=1....N.
How do I accomplish this? thank you for your help.
sum(X[i][j]) = 1 for i=j=1....N

Answer 1

You need a 1d array and call model.sum():
import org.chocosolver.solver.Model;
import org.chocosolver.solver.Solver;
import org.chocosolver.solver.variables.BoolVar;
public class SumBooleans {
private final static int N = 10;
public static void main(String[] args) {
Model model = new Model("Boolean sum");
BoolVar[][] vars = new BoolVar[N][N];
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
vars[i][j] = model.boolVar("vars[" + i + "][" + j + "]");
}
}
BoolVar[] flatArray = new BoolVar[N * N];
for (int index = 0; index < N * N; index++) {
int i = index / N;
int j = index % N;
flatArray[index] = vars[i][j];
}
model.sum(flatArray, "=", 1).post();
//model.sum(flatArray, "<", N).post();
//model.sum(flatArray, ">=", 8).post();
Solver solver = model.getSolver();
if (solver.solve()) {
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) {
System.out.print(vars[i][j].getValue() + " ");
}
System.out.println();
}
}
}
}
Output:
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 1 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0