/*******************************************************************************
* OscaR is free software: you can redistribute it and/or modify
* the Free Software Foundation, either version 2.1 of the License, or
* (at your option) any later version.
*
* OscaR is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU Lesser General Public License  for more details.
*
* You should have received a copy of the GNU Lesser General Public License along with OscaR.
******************************************************************************/
package oscar.examples.cp.hakank

import oscar.cp.modeling._

import oscar.cp.core._
import scala.io.Source._
import scala.math._

/*

Langford's number problem in Oscar.

Langford's number problem (CSP lib problem 24)
http://www.csplib.org/Problems/prob024/
"""
Arrange 2 sets of positive integers 1..k to a sequence,
such that, following the first occurence of an integer i,
each subsequent occurrence of i, appears i+1 indices later
than the last.
For example, for k=4, a solution would be 41312432
"""

* John E. Miller: Langford's Problem
http://www.lclark.edu/~miller/langford.html

* Encyclopedia of Integer Sequences for the number of solutions for each k
http://www.research.att.com/cgi-bin/access.cgi/as/njas/sequences/eisA.cgi?Anum=014552

@author Hakan Kjellerstrand hakank@gmail.com
http://www.hakank.org/oscar/

*/

object Langford {

def main(args: Array[String]) {

val cp = CPSolver()

//
// data
//
val k = if (args.length > 0) args(0).toInt else 4;
val num_to_show = if (args.length > 1) args(1).toInt else 0;

//
// variables
//
val position = Array.fill(2*k)(CPIntVar(0 to 2*k-1)(cp))

// channel positions to a solution array
val solution = Array.fill(2*k)(CPIntVar(1 to k)(cp))

//
// constraints
//
var numSols = 0
cp.solve subjectTo {

for(i <- 1 to k) {
}

// symmetry breaking

} search {

binary(position, _.size, _.min)

} onSolution {
print("solution:" + solution.mkString("") + " ")
println("position:" + position.mkString(""))

numSols += 1

}
println(cp.start(num_to_show))

}

}