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JCP Standard JSR331 “Java Constraint Programming API”. It is used for Modeling and Solving Constraint Satisfaction and Optimization Problems using Java and off-the-shelf Constraint/Linear Solvers

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//=============================================
// J A V A  C O M M U N I T Y  P R O C E S S
// 
// J S R  3 3 1
// 
// Common Implementation
// 
//=============================================
package javax.constraints.impl.selector;

/**
 * This class creates a selector that selects an unbound constrained
 * real variable from a given array of real variables that has the minimal domain size.
 */

import javax.constraints.VarReal;

public class VarRealSelectorMinSize extends VarRealSelectorImpl {

	/**
	 * Constructor from the VarReal[]
	 */
	public VarRealSelectorMinSize(VarReal[] vars) {
		super(vars);
	}

	/**
	 * Returns the index of the unbound real variable with the smallest domain.
	 * If no variables to select, it returns -1;
	 */
	public int select() {
		double minSize = Double.MAX_VALUE;
	    int minIndex = -1;
		for(int i=0; i < getVarReals().length; i++) {
			VarReal var = getVarReals()[i];
			if (var.isBound())
				continue;
			double size = var.getMax() - var.getMin() + 1;
			if (minIndex == -1 || minSize > size) {
				minIndex = i;
				minSize = size;
			}
		}
		return minIndex;
	}

}