poj2365

简单题

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;

#define pi acos(-1)

struct Point
{
    double x, y;
}first, now, last;

int n;
double r;

double dist(Point &a, Point &b)
{
    Point p;
    p.x = a.x - b.x;
    p.y = a.y - b.y;
    return sqrt(p.x * p.x + p.y * p.y);
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d%lf", &n, &r);
    double ans = pi * 2 * r;
    scanf("%lf%lf", &first.x, &first.y);
    last = first;
    for (int i = 1; i < n; i++)
    {
        scanf("%lf%lf", &now.x, &now.y);
        ans += dist(now, last);
        last = now;
    }
    ans += dist(last, first);
    printf("%.2f\n", ans);
    return 0;
}