> 这个代码用float过[scanf和printf用%f],而用double不过[scanf和printf改称%lf]
> 
> 
> #define N 200
> float DP[N][N];
> struct Point {
>   float x, y;
>   Point(float _x=0.0,float _y=0.0):x(_x),y(_y){}
>   bool operator<(const Point &a)const{return x<a.x;}
> };
> 
> float
> dist(const Point & a, const Point & b)
> {
>     return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
> }
> 
> float
> bitonic_eculidean_TSP(vector < Point > &raw)
> {
>   int n=(int)raw.size();
>   sort(raw.begin(),raw.end());
>   memset(DP,0,sizeof(DP));
>   for(int i=1;i<n;i++)DP[i][0]=DP[i-1][0]+dist(raw[i],raw[i-1]);
>   for(int i=2;i<n;i++){
>     for(int j=1;j<i;j++){
>       if((j+1)==i){
> 	DP[i][j]=DP[j][0]+dist(raw[i],raw[0]);
> 	for(int k=1;k<j;k++)
> 	  DP[i][j]=min(DP[i][j],DP[j][k]+dist(raw[i],raw[k]));
>       }else if(i>j+1){
> 	DP[i][j]=DP[i-1][j]+dist(raw[i],raw[i-1]);
>       }
>     }
>   }
>   DP[n-1][n-1]=DP[n-1][0]+dist(raw[0],raw[n-1]);
>   for(int i=1;i<=n-2;i++)DP[n-1][n-1]=min(DP[n-1][n-1],DP[n-1][i]+dist(raw[i],raw[n-1]));
>   return DP[n-1][n-1];
> }
> 
> int
> main()
> {
>   int n;
>   while(scanf("%d",&n)!=EOF){
>     vector<Point>vp;
>     float x,y;
>     for(int i=0;i<n;i++){
>       scanf("%f%f",&x,&y);
>       vp.push_back(Point(x,y));
>     }
>     printf("%.2f\n",bitonic_eculidean_TSP(vp));
>   }
> }