【HDOJ】2440 Watch out the Animal

刚开始学随机算法，凸包+模拟退火。

 /* 2440 */
 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 #define MAXN 105

 typedef struct {
     int x, y;
 } Point_t;

 Point_t stack[MAXN];
 Point_t points[MAXN];
 int dir[][] = {
     {-, }, {, }, {, -}, {, },
     {-, -}, {-, }, {, -}, {, }
 };
 const double eps = 1e-;
 const double next = 0.9;
 int n, top;
 int ans;

 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) + .);
 }

 int Length2(Point_t a, Point_t b) {
     return (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y);
 }

 int cross(Point_t a, Point_t b, Point_t c) {
     return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
 }

 bool comp(Point_t a, Point_t b) {
     int m = cross(points[], a, b);
     return m> || (m== && Length2(points[], a)<Length2(points[], b));
 }

 void Graham() {
     int i, j, k;
     Point_t p;

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

     sort(points+, points+n, comp);
     stack[] = points[];
     stack[] = points[];
     top = ;

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

 double cal(double xx, double yy) {
     double ret = ;
     double x, y;

     for (int i=; i<=top; ++i) {
         x = xx - stack[i].x;
         y = yy - stack[i].y;
         ret += sqrt(x*x + y*y);
     }

     return ret;
 }

 void SA() {
     double step = .;
     double dis, tmp;
     double x, y;
     double xx, yy;
     int i;

     x = stack[].x;
     y = stack[].y;
     dis = cal(x, y);
     while (step > eps) {
         for (i=; i<; ++i) {
             xx = x + step * dir[i][];
             yy = y + step * dir[i][];
             tmp = cal(xx, yy);
             if (tmp < dis) {
                 dis = tmp;
                 x = xx;
                 y = yy;
             }
         }
         step *= next;
     }

     ans = (dis+0.5);
 }

 int main() {
     int t;
     int i, j, k;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         //freopen("data.out", "w", stdout);
     #endif

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

     return ;
 }