poj1113 凸包

#include <iostream>#include <cstdio>#include <cmath>#include <algorithm>using namespace std;const double PI = 3.14159265358979;const int maxn = 1e3+4;struct node{    double x, y;    double rad;}p[maxn], tp[maxn];bool cmp1(node a, node b){    if(a.y == b.y) return a.x < b.x;    return a.y < b.y;}bool cmp2(node a, node b){    if(a.rad == b.rad) return a.x < b.x;    return a.rad < b.rad;}double rad_point(node a, node b){    return atan2((b.y-a.y), (b.x-a.x));}double dist_2point(node a, node b){    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}bool tp_3point(node a, node b, node c){    double m = (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);    if(m > 0) return false;    if(m < 0 || m == 0) return true;}int main(){    #ifndef ONLINE_JUDGE           freopen("in.txt","r",stdin);    #endif // ONLINE_JUDGE    int n;    double r;    while(scanf("%d%lf", &n, &r) != EOF)    {        for(int i = 0; i < n; i++) scanf("%lf%lf", &p[i].x, &p[i].y);        sort(p, p+n, cmp1);        for(int i = 0; i < n; i++) p[i].rad = rad_point(p[0], p[i]);        sort(p+1, p+n, cmp2);        tp[0] = p[0];        tp[1] = p[1];        tp[2] = p[2];        int top = 2;        for(int i = 3; i < n; i++)        {            while(top >= 1 && tp_3point(tp[top-1], tp[top], p[i])) top--;            tp[++top] = p[i];        }        top++;        double dist = 0;        for(int i = 0; i < top; i++) dist += dist_2point(tp[i%top], tp[(i+1)%top]);        double round = 2.0*PI*r;        printf("%.0lf\n", dist+round);    }}