Created
May 10, 2016 13:40
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Compute OEIS sequence A144311; see http://math.stackexchange.com/questions/1779109.
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import java.util.ArrayList; | |
import java.util.List; | |
public class Question1779109 { | |
final static int [] p = {2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97}; | |
final static int maxLength = 2000; | |
final static int ndirect = 7; | |
static int max; | |
public static void main (String [] args) { | |
for (int n = ndirect;;n++) { | |
recurseDirectly (n,0,new int [n]); | |
System.out.println (n + " : " + (max - 1)); | |
} | |
} | |
static void recurseDirectly (int n,int np,int [] residues) { | |
if (np < ndirect) { | |
for (residues [np] = 0;residues [np] < p [np] - 1;residues [np]++) | |
if (residues [np] != 1) | |
recurseDirectly (n,np + 1, residues); | |
} | |
else { | |
List<Integer> remainsList = new ArrayList<Integer> (); | |
outer: | |
for (int r = 1;r <= maxLength;r++) { | |
for (int i = 0;i < ndirect;i++) { | |
int res = (r + residues [i]) % p [i]; | |
if (res == 1 || res == p [i] - 1) | |
continue outer; | |
} | |
remainsList.add (r); | |
} | |
int [] remains = new int [remainsList.size ()]; | |
for (int i = 0;i < remains.length;i++) | |
remains [i] = remainsList.get (i); | |
recurse (n,0,ndirect,remains,new boolean [n],new int [n],residues); | |
} | |
} | |
static void recurse (int n,int d,int nused,int [] remains,boolean [] used,int [] primes,int [] residues) { | |
outer: | |
for (;;) { | |
max = Math.max (max,remains [d]); | |
for (int i = ndirect;i < nused;i++) { | |
int r = (residues [i] + remains [d]) % primes [i]; | |
if (r == 1 || r == primes [i] - 1) { | |
d++; | |
continue outer; | |
} | |
} | |
break; | |
} | |
for (int i = ndirect;i < n;i++) | |
if (!used [i]) | |
for (int r = -1;r <= 1;r += 2) { | |
int res = p [i] - ((r + remains [d] - 1) % p [i] + 1); | |
if (res != 1 && res != p [i] - 1) { | |
residues [nused] = res; | |
primes [nused] = p [i]; | |
used [i] = true; | |
recurse (n,d + 1,nused + 1,remains,used,primes,residues); | |
used [i] = false; | |
} | |
} | |
} | |
} |
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