private void dfs(Digraph G, int v) {
marked[v] = true;
preorder[v] = pre++;
stack1.push(v);
stack2.push(v);
for (int w : G.adj(v)) {
if (!marked[w]) dfs(G, w);
else if (id[w] == -1) {
while (preorder[stack2.peek()] > preorder[w]) stack2.pop();
}
}
// found strong component containing v
if (stack2.peek() == v) {
stack2.pop();
int w;
do {
w = stack1.pop();
id[w] = count;
} while (w != v);
count++;
}
}
