POJ-2365(用例通过，但一直WA，参考的方法没有太看懂)

#include<iostream>
#include<math.h>
#include<stdio.h>
using namespace std;

int main(int argc, char *argv[]){
	int edgeNum;
	double r;
	cin>>edgeNum>>r;

	double x0, y0;
	double perimeter=0;
	double preX, preY;
	double x,y;
	for(int i=0;i<edgeNum;i++){
		if(i==0){
			cin>>x0>>y0;
			preX=x0;
			preY=y0;
		}else{
			cin>>x>>y;

			perimeter+=sqrt(pow(x-preX,2)+pow(y-preY,2));
			preX=x;
			preY=y;
		}
	}

	perimeter+=sqrt(pow(x-x0,2)+pow(y-y0,2));

	perimeter+=2*acos(-1.0)*r;

	printf("%.2lf\n",perimeter);
	return 0;
}

参考文章：

http://blog.youkuaiyun.com/v5zsq/article/details/46827279