Android Open Source - dice-probabilities Cached Cumulative Distribution

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License

The source code is released under:

MIT License

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Java Source Code

package org.kleemann.diceprobabilities.distribution;
// w  w w  . j  a  v a2 s .  com
import org.apache.commons.math3.fraction.BigFraction;

/**
 * <p>
 * This is a simple way to cache values called from
 * Distribution.getCumulativeDistribution() so that the call is O(1) instead of
 * O(n). It should wrapped around a distribution after all the sums and
 * multiplies are done.
 */
class CachedCumulativeDistribution extends AbstractDistribution {

  private final Distribution d;
  private final BigFraction[] cums;

  CachedCumulativeDistribution(Distribution d) {
    this.d = d;
    if (d.lowerBound() < d.upperBound()) {
      cums = new BigFraction[d.upperBound() - d.lowerBound()];
      int i = cums.length - 1;
      cums[i] = d.getProbability(d.upperBound() - 1);
      --i;
      for (int x = d.upperBound() - 2; x >= d.lowerBound(); --x, --i) {
        cums[i] = cums[i + 1].add(d.getProbability(x));
      }
    } else {
      cums = null;
    }
  }

  @Override
  public int lowerBound() {
    return d.lowerBound();
  }

  @Override
  public int upperBound() {
    return d.upperBound();
  }

  @Override
  public BigFraction getProbability(int x) {
    return d.getProbability(x);
  }

  @Override
  public BigFraction getCumulativeProbability(int x) {
    if (x < d.lowerBound()) {
      return BigFraction.ONE;
    } else if (x >= d.upperBound()) {
      return BigFraction.ZERO;
    } else {
      return cums[x - d.lowerBound()];
    }
  }

  /**
   * <p>
   * This class has an efficient getCumulativeProbability(x)
   */
  @Override
  public Distribution cacheCumulative() {
    return this;
  }
}

Java Source Code List