benchmark_type mcss_bench() {
long n = pasl::util::cmdline::parse_or_default_long("n", 1l<<20);
sparray* inp = new sparray(0);
value_type* outp = new value_type;
auto init = [=] {
*inp = gen_random_sparray(n);
};
auto bench = [=] {
*outp = mcss(*inp);
};
auto output = [=] {
std::cout << "result " << *outp << std::endl;
};
auto destroy = [=] {
delete inp;
delete outp;
};
return make_benchmark(init, bench, output, destroy);
}
sumnode mcss(int *a, int left, int right)
{
sumnode leftsum, rightsum, mtlsum, mtrsum, thissum, tempsum;
if (right - left <= 1)
{
thissum.sum = a[left];
thissum.left = left;
thissum.right = right;
return thissum;
}
else
{
leftsum = mcss(a, left, (right + left) / 2);
rightsum = mcss(a, (right + left) / 2, right);
if (leftsum.right == rightsum.left)
{
thissum.left = leftsum.left;
thissum.right = rightsum.right;
thissum.sum = leftsum.sum + rightsum.sum;
}
else
{
mtlsum.sum = 0; mtlsum.left = mtlsum.right = (left + right) / 2;
mtrsum.sum = 0; mtrsum.left = mtrsum.right = (left + right) / 2;
tempsum.sum = 0;
for (int i = (left + right) / 2 - 1; i >= leftsum.left ; --i)
{
tempsum.sum += a[i];
if (tempsum.sum > mtlsum.sum)
{
mtlsum.sum = tempsum.sum;
mtlsum.left = i;
}
}
tempsum.sum = 0;
for (int i = (left + right) / 2; i < rightsum.right ; ++i)
{
tempsum.sum += a[i];
if (tempsum.sum > mtrsum.sum)
{
mtrsum.sum = tempsum.sum;
mtrsum.right = i + 1;
}
}
thissum.sum = 0; thissum.left = thissum.right = (left + right) / 2;
if (mtlsum.sum > 0)
{
thissum.sum += mtlsum.sum;
thissum.left = mtlsum.left;
}
if (mtrsum.sum > 0)
{
thissum.sum += mtrsum.sum;
thissum.right = mtrsum.right;
}
}
if (thissum.sum > leftsum.sum)
return (thissum.sum > rightsum.sum) ? thissum : rightsum;
else
return (leftsum.sum > rightsum.sum) ? leftsum : rightsum;
}
}
