void lcs(seq const & xs, seq const & ys, seq & an_lcs)
{
members xs_in_lcs(xs.size(), false);
calculate_lcs(xs.begin(), xs.begin(), xs.end(),
ys.begin(), ys.end(), xs_in_lcs);
set_lcs(xs.begin(), xs_in_lcs, back_inserter(an_lcs));
}
void
calculate_lcs(it xo, it xlo, it xhi, it ylo, it yhi, members & xs_in_lcs)
{
unsigned const nx = distance(xlo, xhi);
if (nx == 0)
{
// empty range. all done
}
else if (nx == 1)
{
// single item in x range.
// If it's in the yrange, mark its position in the LCS
xs_in_lcs[distance(xo, xlo)] = find(ylo, yhi, *xlo) != yhi;
}
else
{
// split the xrange
it xmid = xlo + nx / 2;
// Find LCS lengths at xmid, working from both ends of the range
lengths ll_b, ll_e;
std::reverse_iterator<it> hix(xhi), midx(xmid), hiy(yhi), loy(ylo);
lcs_lens(xlo, xmid, ylo, yhi, ll_b);
lcs_lens(hix, midx, hiy, loy, ll_e);
// Find the optimal place to split the y range
lengths::const_reverse_iterator e = ll_e.rbegin();
int lmax = -1;
it y = ylo, ymid = ylo;
for (lengths::const_iterator b = ll_b.begin();
b != ll_b.end(); ++y, ++b, ++e)
{
if (*b + *e > lmax)
{
lmax = *b + *e;
ymid = y;
}
}
// Split the range and recurse
calculate_lcs(xo, xlo, xmid, ylo, ymid, xs_in_lcs);
calculate_lcs(xo, xmid, xhi, ymid, yhi, xs_in_lcs);
}
}
int main(int argc, char **argv)
{
char *a = "BDCABA";
char *b = "ABCBDAB";
int lcs;
lcs = calculate_lcs(a, b);
printf("LCS is %d\n", lcs);
return 0;
}
