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ocelli-core developed by Netflix

There is a newer version: 0.1.0-rc.2

package netflix.ocelli.selectors;

import java.util.Collections;
import java.util.List;
import java.util.Random;

/**
 * Select the next element using a random number.  
 * 
 * The weights are sorted such as that each cell in the array represents the
 * sum of the previous weight plus it's weight.
 * 
 * Worst case runtime complexity is O(log N)
 * 
 * @author elandau
 *
 */
public class RandomWeightSelector implements WeightSelector {

    private Random random = new Random();
    
    @Override
    public Integer call(List weights, Integer count) {
        int next = random.nextInt(count);
        int pos = Collections.binarySearch(weights, next);
        if (pos >= 0) {
            return pos+1;
        }
        else {
            return -(pos) - 1;
        }

    }
}