%Tikz画图
\usepackage{tikz}
\usetikzlibrary{arrows,graphs} %指明是图库
\begin{tikzpicture}[> = stealth, % arrow head style
shorten > = 1pt, % don't touch arrow head to node
auto,
node distance = 3cm, % distance between nodes
semithick % line style
,scale=.8,auto=left,every node/.style={circle,fill=blue!20}]
\node (n1) at (0,0) {1};
\node (n2) at (0,-2) {2};
\node (n3) at (0,-4) {3};
\node (n4) at (0,-6) {4};
\node (n5) at (0,-8) {5};
\draw (n1)--(n2);
\draw (n2)--(n3);
\draw (n3)--(n4);
\draw [red,very thick](n4)--(n5);
\draw [red,very thick] (n1) .. controls (-2,-2.5) ..(n4);
\draw [red,very thick](n1) .. controls (2,-3.5) ..(n5);
\end{tikzpicture}
