POJ2677 Tour[DP 状态规定]

//
//  main.cpp
//  poj2677
//
//  Created by Candy on 10/18/16.
//  Copyright © 2016 Candy. All rights reserved.
//

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
using namespace std;
typedef long long ll;
const int N=1005,INF=1e9;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1;c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘;c=getchar();}
    return x*f;
}
int n,x[N],y[N];
double d[N][N];
inline double dis(int i,int j){
    return sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
}
void dp(){
    d[n][n-1]=dis(n,n-1);
    for(int i=n;i>=1;i--)
        for(int j=i-1;j>=1;j--){
            if(i+1<=n)d[i][j]=min(d[i+1][j]+dis(i,i+1),d[i+1][i]+dis(j,i+1));
            else if(i!=n||j!=n-1) d[i][j]=INF;
            //printf("d %d %d %f\n",i,j,d[i][j]);
        }
}
int main(int argc, const char * argv[]) {
    while(scanf("%d",&n)!=EOF){
        for(int i=1;i<=n;i++) x[i]=read(),y[i]=read();
        dp();
        printf("%.2f\n",d[2][1]+dis(1,2));
    }
    
    return 0;
}