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A036233.java
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package irvine.oeis.a036;
import java.util.ArrayList;
import java.util.HashSet;
import irvine.math.function.Functions;
import irvine.math.z.Z;
import irvine.oeis.Sequence1;
/**
* A036233 Inverse Colombian function.
* @author Sean A. Irvine
*/
public class A036233 extends Sequence1 {
private static final class State {
private final HashSet<Long> mMembers = new HashSet<>();
private final long mHead;
private long mTail;
private State(final long start) {
mHead = start;
mTail = start;
mMembers.add(mHead);
}
}
private final ArrayList<State> mA = new ArrayList<>();
private long mN = 0;
@Override
public Z next() {
++mN;
for (final State sumSeq : mA) {
if (sumSeq.mTail < mN) {
sumSeq.mTail += Functions.DIGIT_SUM.l(sumSeq.mTail);
sumSeq.mMembers.add(sumSeq.mTail);
}
if (sumSeq.mMembers.contains(mN)) {
return Z.valueOf(sumSeq.mHead);
}
}
mA.add(new State(mN));
return Z.valueOf(mN);
}
}