【HDOJ】1348 Wall

计算几何-凸包模板题目，Graham算法解。

 /* 1348 */
 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 #define MAXN 1005

 typedef struct Point_t {
     double x, y;
     Point_t() {}
     Point_t(double xx, double yy) {
         x = xx; y = yy;
     }
 } Point_t;

 Point_t stack[MAXN];
 Point_t points[MAXN];
 const double PI = acos(-1.0);
 int n;

 double Length(Point_t a, Point_t b) {
     return sqrt((a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
 }

 double cross(Point_t p0, Point_t p1, Point_t p2) {
     return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
 }

 bool comp(Point_t a, Point_t b) {
     double k = cross(points[], a, b);
     return !(k< || (k== && Length(points[], a)>Length(points[], b)));
 }

 double Graham() {
     double ret = ;
     int i, j, k;
     int top;
     Point_t p0;

     p0 = points[];
     k = ;
     for (i=; i<n; ++i) {
         if (points[i].x<p0.x || (points[i].x==p0.x && points[i].y<p0.y)) {
             p0 = points[i];
             k = i;
         }
     }

     points[k] = points[];
     points[] = p0;
     sort(points+, points+n, comp);

     stack[] = points[];
     stack[] = points[];
     stack[] = points[];
     top = ;
     for (i=; i<n; ++i) {
         while (cross(stack[top-], stack[top], points[i])<= && top>)
             --top;
         stack[++top] = points[i];
     }
     stack[++top] = p0;
     for (i=; i<=top; ++i)
         ret += Length(stack[i-], stack[i]);

     return ret;
 }

 int main() {
     int t;
     int i, j, k, tmp;
     double l, ans;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
     #endif

     scanf("%d", &t);
     while (t--) {
         scanf("%d %lf", &n, &l);
         for (i=; i<n; ++i)
             scanf("%lf %lf", &points[i].x, &points[i].y);
         ans = Graham();
         ans += PI * (l+l);
         printf("%.0lf\n", ans);
         if (t)
             printf("\n");
     }

     return ;
 }