poj 2253 Frogger

这道题我是用并查集处理的，将所有边排序，当生成树里出现第一个点，第二个点时（或第0点第1个点），结束并查集，输出已处理边里的最大值就可以了。

 1 #include<stdio.h>

 2 #include<stdlib.h>

 3 #include<math.h>

 4 #define MAXN 210

 5 int n,g,h,u[MAXN*MAXN],v[2*MAXN*MAXN],p[MAXN],r[2*MAXN*MAXN];

 6 double x[MAXN],y[MAXN],w[2*MAXN*MAXN],flag[2*MAXN*MAXN];

 7 

 8 int cmp(const void *_p, const void *_q)

 9 {

10     int *p = (int *)_p;

11     int *q = (int *)_q;

12     return w[*p]>w[*q] ? 1 : -1;

13 }

14 int find(int x2){return p[x2] == x2 ? x2 : p[x2] = find(p[x2]);}

15 void kruskal()

16 {

17     double ans = -1;

18     int ok1 = 0, ok2 = 0;

19     for(int i = 0; i < n; i ++) p[i] = i;

20     for(int i = 0; i < h; i ++) r[i] = i;

21     qsort(r,h,sizeof(r[0]),cmp);

22     g = 0;

23     for(int i = 0; i < h; i ++)

24     {

25         int e = r[i];

26         int x1 = find(u[e]), y1 = find(v[e]);

27         if(find(0) == find(1))break;

28         if(x1 != y1)

29         {

30             p[x1] = y1;

31             flag[g ++] = w[e];

32          }

33     }

34     for(int i = 0; i < g; i ++)

35     {

36         if(flag[i] > ans) ans = flag[i];

37     }

38     printf("Frog Distance = %.3f\n\n",ans);

39 }

40 void init()

41 {

42     int num = 1;

43     while(~scanf("%d",&n))

44     {

45         if(n == 0) break;

46         for(int i = 0; i < n; i ++)

47             scanf("%lf%lf",&x[i], &y[i]);

48         h = 0;

49         for(int i = 0; i < n; i ++)

50             for(int j = i+1; j < n; j ++)

51             {

52                 double dis = sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));

53                 u[h] = i, v[h] = j, w[h++] = dis;

54                 u[h] = j; v[h] = i, w[h++] = dis;

55             }

56             printf("Scenario #%d\n",num++);

57         kruskal();    

58     }    

59 }

60 

61 int main()

62 {

63     init();

64     return 0;

65 }