(UVA) Station Balance - Solution

Link to the problem: https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=351

We need to try all the possible combinations for putting a specimen in a chamber. 


import java.io.*;
import java.util.*;
import java.text.DecimalFormat;  

class Main {
    public int numChambers;
    public int numSpecimens;
    public double averageMass;
    public int[] specimensMass;
    public ArrayList<ArrayList<Integer>> chambersContent;
    public ArrayList<ArrayList<Integer>> chambersContentBetter;
    public double imbalanceBetter;
   
    public double calcImbalance() {
        double imbalance = 0;
        for (int i = 0; i < numChambers; i++) {
            double sumMass = 0;
            for (int j = 0; j < chambersContent.get(i).size(); j++) {
                sumMass += chambersContent.get(i).get(j);
            }
            imbalance += (Math.abs(sumMass-averageMass));
        }
       
        return imbalance;
    }
   
    public void rec(int specimenID) {
        if (specimenID == numSpecimens) {
            double imbalance = calcImbalance();
            if (imbalance < imbalanceBetter) {
                imbalanceBetter = imbalance;
                for (int i = 0; i < numChambers; i++) {
                    chambersContentBetter.set(i, (ArrayList<Integer>) chambersContent.get(i).clone());
                }
            }
            return;
        }
       
        boolean putEmpty = false;
        for (int j = 0; j < numChambers; j++) {
            if (chambersContent.get(j).size() == 2) {
                continue;
            }
            if (chambersContent.get(j).size() == 0) {
                if (putEmpty) {
                    continue;
                }
                putEmpty = true;
            }
            chambersContent.get(j).add(specimensMass[specimenID]);
            rec(specimenID+1);
            chambersContent.get(j).remove(chambersContent.get(j).size()-1);
        }
    }
   
    public void process() throws NumberFormatException, IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
       
        int numCase = 0;
        String line = br.readLine();
        while (line != null) {
            String[] s = line.split("\\s");
            numChambers = Integer.parseInt(s[0]);
            numSpecimens = Integer.parseInt(s[1]);

            double sumMass = 0;
            specimensMass = new int[numSpecimens];
            line = br.readLine();
            s = line.split("\\s");
            for (int i = 0; i < numSpecimens; i++) {
                specimensMass[i] = Integer.parseInt(s[i]);
                sumMass += specimensMass[i];
            }
            averageMass = sumMass/numChambers;
           
            chambersContent = new ArrayList<>();
            chambersContentBetter = new ArrayList<>();
            for (int i = 0; i < numChambers; i++) {
                chambersContent.add(new ArrayList<Integer>());
                chambersContentBetter.add(new ArrayList<Integer>());
            }
            imbalanceBetter = 20000000.0;
            rec(0);

            bw.write("Set #" + ++numCase + "\n");
            for (int i = 0; i < numChambers; i++) {
                bw.write(" " + i + ":");
                for (int j = 0; j < chambersContentBetter.get(i).size(); j++) {
                    bw.write(" " + chambersContentBetter.get(i).get(j));
                }
                bw.write("\n");
            }
            DecimalFormat df = new DecimalFormat("0.00000");
            bw.write("IMBALANCE = " + df.format(imbalanceBetter) + "\n\n");
       
            line = br.readLine();
        }
       
        bw.flush();
        bw.close();
       
        return;
    }
   
    public static void main(String[] args) throws NumberFormatException, IOException {
        Main m = new Main();
        m.process();
       
        System.exit(0);
    }
}