【HDOJ】3285 Convex Hull of Lattice Points

凸包模板题目。

 /* 3285 */
 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 #define MAXN 55

 typedef struct {
     int x, y;
 } Point_t;

 Point_t points[MAXN];
 Point_t stack[MAXN];
 int top;

 void output(int);

 double dist(Point_t a, Point_t b) {
     return sqrt(1.0*(a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y));
 }

 int dist2(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== && dist2(points[], a)<dist2(points[], b));
 }

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

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

 int main() {
     int t, case_n;
     int n;
     int i, j, k;
     Point_t p;

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

     scanf("%d", &t);
     while (t--) {
         scanf("%d %d", &case_n, &n);
         for (i=; i<n; ++i)
             scanf("%d %d", &points[i].x, &points[i].y);
         Graham(n);
         printf("%d %d\n", case_n, top+);
         p = stack[];
         k = ;
         for (i=; i<=top; ++i) {
             if (stack[i].y>p.y || (stack[i].y==p.y && stack[i].x<p.x)) {
                 p = stack[i];
                 k = i;
             }
         }
         for (i=k; i>=; --i)
             printf("%d %d\n", stack[i].x, stack[i].y);
         for (i=top; i>k; --i)
             printf("%d %d\n", stack[i].x, stack[i].y);
     }

     return ;
 }