Problem14.java

package com.javamultiplex.projecteuler;

import java.util.ArrayList;
import java.util.List;

/**
 * 
 * @author Rohit Agarwal
 * @category Project Euler Problems
 * @Problem 14 - Longest Collatz Sequence.
 *
 */
public class Problem14 {

	public static void main(String[] args) {

		int limit = 1000000; // Limit is one million
		int size = 0, max = 1, j = 0;
		for (int i = 2; i < limit; i++) {
			size = getChainSize(i);
			if (size > max) {
				max = size;
				j = i;
			}
		}
		System.out.println("Starting number, under one million, produces the longest chain is : " + j);
	}

	private static int getChainSize(int n) {

		long num = n;
		List<Long> list = new ArrayList<>();
		int size = 0;
		while (num != 1) {
			list.add(num);
			/*
			 * As per Collatz sequence condition, if num is even then num=num/2
			 * else num=3*num+1
			 */
			if (num % 2 == 0) {
				num = num / 2;
			} else {
				num = 3 * num + 1;
			}
		}
		size = list.size();
		return size;
	}

}