if WA#13#21#22，缩点记录出度时不能这样

for (int i=1; i<=m; ++i) 
		du[scc[a[i]]]+=(scc[a[i]]!=scc[b[i]]);

要这样

for (int i=1; i<=n; ++i)
		for (int j:e[i])
			du[scc[i]]+=(scc[i]!=scc[j]);