CS426 - Operating Systems

Collatz assignment

The Collatz conjecture is simple. It says that for every starting number the sequence below always eventually gets to a 1. f(n) = n/2 if n is even f(n+1) = 3n+1 if n is odd

For example. 17 -> 52 -> 26 -> 13 -> 40 -> 20 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1

Your mission is to find the starting number that is less than 1,000,000 with the longest sequence.

This might take a long time. To make it faster, you might cache previous answers. Suppose you have an array prev[]. Prev[n] is the length of the sequence starting at n. If, when computing a sequence, you ever get to a number with a value in prev[], you can use that instead of continuing the computation.

If you have multiple threads, you must use good locking.

Objectives

• Can compute the collatz sequence length for a given number.
• Can find the longest sequence.
• Uses Java threads
• Uses C++ Threads
• Uses the array prev[] above.
• Does better load balancing that simple partitioning.