nyist_78_圈水池

 1 #include <cmath>

 2 #include <cstdio>

 3 #include <cstdlib>

 4 #include <iostream>

 5 

 6 using  namespace std;

 7 

 8 const int N = 105;

 9 

10 struct point {

11     long long x, y;

12 }p[N];

13 

14 long long dis(point A, point B) {//两点距离 

15     return (long long)sqrt((A.x - B.x) * (A.x - B.x) + (A.y - B.y) * (A.y - B.y));

16 }

17 

18 long long crossProd(point A, point B, point C) {//叉乘 

19     return (B.x - A.x) * (C.y - A.y) - (B.y - A.y) * (C.x - A.x);

20 }

21 

22 int cmp1(const void *a, const void *b) {

23     point *c = (point *)a;

24     point *d = (point *)b;

25     long long k = crossProd(p[0], *c, *d);

26     if (k < 0 || (!k && dis(p[0], *c) > dis(p[0], *d))) return 1;

27     return -1;

28 }

29 

30 int cmp2(const void *a, const void *b) {

31     point *c = (point *)a;

32     point *d = (point *)b;

33     if (c->x != d->x) return (int)(c->x - d->x);

34     return (int)(c->y - d->y);

35 }

36 

37 int Graham(point p[], int n) {//求凸包，返回凸包顶点个数 

38     long long x = p[0].x;

39     long long y = p[0].y;

40     int mi = 0;

41     for (int i=1; i<n; ++i) {

42         if (p[i].y < y || (p[i].y == y && p[i].x < x)) {

43             x = p[i].x;

44             y = p[i].y;

45             mi = i;

46         }

47     } 

48     point tmp = p[0];

49     p[0] = p[mi];

50     p[mi] = tmp;

51     qsort(p+1, n-1, sizeof(point), cmp1);



52     int top = 1;

53     for (int i=2; i<n; ++i) {

54         while (crossProd(p[top-1], p[top], p[i]) <= 0 && top >= 1) --top;

55         p[++top] = p[i];

56     }

57     return top + 1;

58 }

59 

60 void solve(point p[], int n) {

61     int top = Graham(p, n);

62     qsort(p, top, sizeof(point), cmp2);

63     for (int i=0; i<top; ++i) printf ("%lld %lld\n", p[i].x, p[i].y);

64 }

65 

66 int main() {

67     int t;

68     scanf ("%d", &t);

69     while (t--) {

70         int n;

71         scanf ("%d", &n);

72         for (int i=0; i<n; ++i) scanf ("%lld%lld", &p[i].x, &p[i].y);

73         solve(p, n);

74     }

75     return 0;

76 }