Project Euler 14: Longest Collatz Sequence

Project-Euler-14.java

package ca.i88.it.euler;


public class ProjectEuler14 {
	public static void main(String[] args) {
		long start = System.currentTimeMillis();
		final int number = 1000000;

		int sequenceLength = 0;
		int startingNumber = 0;
		long sequence;

		int[] cache = new int[number + 1];


		for (int i = 3; i <= number; i = i + 2) {
			sequence = i;
			int k = 0;
			while (sequence != 1 && sequence >= i) {
				k++;
				if ((sequence % 2) == 0) {
					sequence = sequence / 2;
				} else {
					sequence = sequence * 3 + 1;
				}
			}
			// Store result in cache
			cache[i] = k + cache[(int) sequence];

			// Check if sequence is the best solution
			if (cache[i] > sequenceLength) {
				sequenceLength = cache[i];
				startingNumber = i;
			}
		}
		long end = System.currentTimeMillis();

		System.out.println(startingNumber);
		System.out.println(end - start);
	}
}