【HDOJ】2440 Watch out the Animal

刚开始学随机算法，凸包+模拟退火。
  1 /* 2440 */
  2 #include <iostream>
  3 #include <cstdio>
  4 #include <cstring>
  5 #include <cstdlib>
  6 #include <cmath>
  7 #include <algorithm>
  8 using namespace std;
  9 
 10 #define MAXN 105
 11 
 12 typedef struct {
 13     int x, y;
 14 } Point_t;
 15 
 16 Point_t stack[MAXN];
 17 Point_t points[MAXN];
 18 int dir[8][2] = {
 19     {-1, 0}, {1, 0}, {0, -1}, {0, 1},
 20     {-1, -1}, {-1, 1}, {1, -1}, {1, 1}
 21 };
 22 const double eps = 1e-10;
 23 const double next = 0.9;
 24 int n, top;
 25 int ans;
 26 
 27 double Length(Point_t a, Point_t b) {
 28     return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) + 0.);
 29 }
 30 
 31 int Length2(Point_t a, Point_t b) {
 32     return (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y);
 33 }
 34 
 35 int cross(Point_t a, Point_t b, Point_t c) {
 36     return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
 37 }
 38 
 39 bool comp(Point_t a, Point_t b) {
 40     int m = cross(points[0], a, b);
 41     return m>0 || (m==0 && Length2(points[0], a)<Length2(points[0], b));
 42 }
 43 
 44 void Graham() {
 45     int i, j, k;
 46     Point_t p;
 47     
 48     p = points[0];
 49     k = 0;
 50     for (i=1; i<n; ++i) {
 51         if (points[i].x<p.x || (points[i].x==p.x && points[i].y<p.y)) {
 52             k = i;
 53             p = points[i];
 54         }
 55     }
 56     points[k] = points[0];
 57     points[0] = p;
 58     
 59     sort(points+1, points+n, comp);
 60     stack[0] = points[0];
 61     stack[1] = points[1];
 62     top = 1;
 63     
 64     for (i=2; i<n; ++i) {
 65         while (top>1 && cross(stack[top-1], stack[top], points[i])<=0)
 66             --top;
 67         stack[++top] = points[i];
 68     }
 69 }
 70 
 71 double cal(double xx, double yy) {
 72     double ret = 0;
 73     double x, y;
 74     
 75     for (int i=0; i<=top; ++i) {
 76         x = xx - stack[i].x;
 77         y = yy - stack[i].y;
 78         ret += sqrt(x*x + y*y);
 79     }
 80     
 81     return ret;
 82 }
 83 
 84 void SA() {
 85     double step = 10000.;
 86     double dis, tmp;
 87     double x, y;
 88     double xx, yy;
 89     int i;
 90 
 91     x = stack[0].x;
 92     y = stack[0].y;
 93     dis = cal(x, y);
 94     while (step > eps) {
 95         for (i=0; i<8; ++i) {
 96             xx = x + step * dir[i][0];
 97             yy = y + step * dir[i][1];
 98             tmp = cal(xx, yy);    
 99             if (tmp < dis) {
100                 dis = tmp;
101                 x = xx;
102                 y = yy;
103             }
104         }
105         step *= next;
106     }
107     
108     ans = (dis+0.5);
109 }
110 
111 int main() {
112     int t;
113     int i, j, k;
114     
115     #ifndef ONLINE_JUDGE
116         freopen("data.in", "r", stdin);
117         //freopen("data.out", "w", stdout);
118     #endif
119     
120     scanf("%d", &t);
121     while (t--) {
122         scanf("%d", &n);
123         for (i=0; i<n; ++i)
124             scanf("%d %d", &points[i].x, &points[i].y);
125         Graham();
126         SA();
127         printf("%d
", ans);
128         if (t)
129             printf("
");
130     }
131     
132     return 0;
133 }