Algorithm $DFS(G)$ :

for each vertex $v$

do visited $(v)=$ false

endfor;

clock $=1$;

for each vertex $v$

do if visited $(v)=$ false

then EXPLORE $(v)$

endif

endfor

Algorithm EXPLore $(v)$ :

visited$(v)=$ true;

pre$(v)=$ clock;

clock $=$ clock $+1$ ;

for each edge $(v,u)$

do if visited $(u)=$ false

then ExplorE $(u)$

endif

endfor;

post$(v)=$ clock;

clock $=$ clock $+1$