scc

import std.algorithm, std.typecons;
alias E = Tuple!(int, "to");
E[][] g = new E[][5];
g[0] ~= E(1);
g[1] ~= E(2);
g[2] ~= E(0); g[2] ~= E(3);
g[3] ~= E(4);
g[4] ~= E(3);

auto info = scc(g);

assert(info.id[0] == info.id[1] && info.id[1] == info.id[2]);
assert(info.id[3] == info.id[4]);
assert(info.id[0] < info.id[3]); //idはトポロジカル順
assert(equal(info.group(0).dup.sort!"a<b", [0, 1, 2]));
assert(equal(info.group(3).dup.sort!"a<b", [3, 4]));