\def\n{6}
\def\radius{2cm}

\begin{tikzpicture}[NPC/.style = {color=white, draw, fill=black}, P/.style = {draw=black}]
    \foreach \i/\kind [count=\xi] in {a/NPC,b/P,c/NPC,d/NPC,e/P,f/NPC} 
        \node[\kind, circle] (\i) at ({-360/\n * (\xi)}:\radius) {$\Pi_\i$};
	
    \foreach \u/\v in {a/c,a/d,a/f,c/d,c/f,d/f,b/c,b/d,b/e,b/f,e/f,f/a,f/c,f/d,d/c,d/a,c/a,e/b,b/a,e/d,e/c,e/a}
        \draw[->] (\u) edge[bend right=10] (\v);
    \foreach \u/\v in {}
        \draw[->] (\u) edge[bend right=10] (\v);
        
    \node[NPC, circle, label={right:Problem \NPC}] at (4, .5) {$\Pi$};
    \node[P, circle, label={right:Problem \P}] at (4, -.5) {$\Pi$};
\end{tikzpicture}