Main.java Source code

Introduction

Here is the source code for Main.java

Source

//package com.java2s;
//License from project: Apache License 

import java.util.stream.LongStream;

public class Main {
    /**
     * Applies the Collatz conjecture on <code>value</code>, and count the steps to reach 1.
     * <p>
     * Examples:
     * <ul>
     * <li>1: 1 &#8594; 4 &#8594; 2 &#8594; 1. Therefore, the return value is 3.</li>
     * <li>2: 2 &#8594; 1. Therefore, the return value is 1.</li>
     * </ul>
     * <p>
     * This implementation works by using a {@link Stream#anyMatch(java.util.function.Predicate)}
     * short-circuiting terminal operation, so although the right answer is returned at the end, it
     * does alter the definition of a stream of Collatz sequence numbers.
     *
     * @param value the value to start from.
     * @return the number of steps to end at 1.
     * @throws IllegalArgumentException if <code>value</code> is 0 or less.
     */
    public static long stepsFor(long value) {
        if (value <= 0) {
            throw new IllegalArgumentException("Input must be greater than 0.");
        }
        final long[] result = new long[1];
        LongStream.iterate(value, v -> ++result[0] > 0 && v % 2 == 0 ? v / 2 : 3 * v + 1)
                .anyMatch(v -> v == 1 && result[0] > v);
        return --result[0];
    }
}