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80 lines
2.7 KiB
80 lines
2.7 KiB
package fr.mieuxvoter.mj;
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import java.math.BigInteger;
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import java.security.InvalidParameterException;
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/**
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* The deliberator expects the proposals' tallies to hold the same amount of judgments.
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* This NormalizedTally accepts tallies with disparate amounts of judgments per proposal,
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* and normalizes them to their least common multiple, which amounts to using percentages,
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* except we don't use floating-point arithmetic.
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*
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* This is useful when there are too many proposals for judges to be expected to judge them all,
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* and all the proposals received reasonably similar amounts of judgments.
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*/
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public class NormalizedTally extends Tally implements TallyInterface {
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public NormalizedTally(ProposalTallyInterface[] proposalsTallies) {
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super(proposalsTallies);
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initializeFromProposalsTallies(proposalsTallies);
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}
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public NormalizedTally(TallyInterface tally) {
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super(tally.getProposalsTallies());
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initializeFromProposalsTallies(tally.getProposalsTallies());
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}
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protected void initializeFromProposalsTallies(ProposalTallyInterface[] proposalsTallies) {
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Integer amountOfProposals = getAmountOfProposals();
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// Compute the Least Common Multiple
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BigInteger amountOfJudges = BigInteger.ONE;
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for (ProposalTallyInterface proposalTally : proposalsTallies) {
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amountOfJudges = lcm(amountOfJudges, proposalTally.getAmountOfJudgments());
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}
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if (0 == amountOfJudges.compareTo(BigInteger.ZERO)) {
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throw new InvalidParameterException("Cannot normalize: one or more proposals have no judgments.");
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}
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// Normalize proposals to the LCM
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ProposalTally[] normalizedTallies = new ProposalTally[amountOfProposals];
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for (int i = 0 ; i < amountOfProposals ; i++) {
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ProposalTallyInterface proposalTally = proposalsTallies[i];
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ProposalTally normalizedTally = new ProposalTally(proposalTally);
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BigInteger factor = amountOfJudges.divide(proposalTally.getAmountOfJudgments());
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Integer amountOfGrades = proposalTally.getTally().length;
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BigInteger[] gradesTallies = normalizedTally.getTally();
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for (int j = 0 ; j < amountOfGrades; j++) {
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gradesTallies[j] = gradesTallies[j].multiply(factor);
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}
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normalizedTallies[i] = normalizedTally;
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}
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setProposalsTallies(normalizedTallies);
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setAmountOfJudges(amountOfJudges);
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}
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/**
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* Least Common Multiple
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*
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* http://en.wikipedia.org/wiki/Least_common_multiple
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*
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* lcm( 6, 9 ) = 18
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* lcm( 4, 9 ) = 36
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* lcm( 0, 9 ) = 0
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* lcm( 0, 0 ) = 0
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*
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* @author www.java2s.com
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* @param a first integer
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* @param b second integer
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* @return least common multiple of a and b
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*/
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public static BigInteger lcm(BigInteger a, BigInteger b) {
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if (a.signum() == 0 || b.signum() == 0)
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return BigInteger.ZERO;
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return a.divide(a.gcd(b)).multiply(b).abs();
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}
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}
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