Project Euler (P14): recursion problems
- by sean mcdaid
Hi I'm doing the Collatz sequence problem in project Euler (problem 14). My code works with numbers below 100000 but with numbers bigger I get stack over-flow error.
Is there a way I can re-factor the code to use tail recursion, or prevent the stack overflow. The code is below:
import java.util.*;
public class v4
{
// use a HashMap to store computed number, and chain size
static HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
public static void main(String[] args)
{
hm.put(1, 1);
final int CEILING_MAX=Integer.parseInt(args[0]);
int len=1;
int max_count=1;
int max_seed=1;
for(int i=2; i<CEILING_MAX; i++)
{
len = seqCount(i);
if(len > max_count)
{
max_count = len;
max_seed = i;
}
}
System.out.println(max_seed+"\t"+max_count);
}
// find the size of the hailstone sequence for N
public static int seqCount(int n)
{
if(hm.get(n) != null)
{
return hm.get(n);
}
if(n ==1)
{
return 1;
}
else
{
int length = 1 + seqCount(nextSeq(n));
hm.put(n, length);
return length;
}
}
// Find the next element in the sequence
public static int nextSeq(int n)
{
if(n%2 == 0)
{
return n/2;
}
else
{
return n*3+1;
}
}
}
