hdu 1811 二分+并查集

 1 #include "stdio.h"  //二分+并查集，，想想道理何在！

 2 #include "stdlib.h"

 3 #include "algorithm"

 4 using namespace std;

 5 #define INF 0x3fffffff

 6 struct node{

 7     int x,y,dis;

 8 }a[1005];

 9 

10 int set[1005];

11 

12 int find(int x){

13     if(set[x]!=x)

14         set[x] = find(set[x]);

15     return set[x];        

16 }

17 

18 int cmp(node u,node v)

19 {

20     return u.dis < v.dis;    

21 }

22 

23 void Union(int x,int y)

24 {        

25     set[find(x)] = find(y);        

26 } 

27 

28 void init(int n) 

29 {

30     int i;

31     for(i=1;i<=n;i++)

32         set[i] = i;    

33 }

34 

35 int main()

36 {

37     int i,j;

38     int n,m,q;

39     while(scanf("%d%d",&n,&m)!=-1)

40     {

41         int x,y,k;

42         for(i=0;i<m;i++)

43         {

44             scanf("%d%d%d",&x,&y,&k);

45             a[i].x = x;

46             a[i].y = y;

47             a[i].dis = k;

48         }

49         sort(a,a+m,cmp);

50         scanf("%d",&q);

51         int min;

52         while(q--)

53         {

54             scanf("%d%d",&x,&y);

55             min = INF;

56             for(i=0;i<m;i++)

57             {

58                 init(n);

59                 for(j=i;j<m;j++)

60                 {

61                     Union(a[j].x,a[j].y);

62                     if(find(x) == find(y))

63                         break;

64                 }

65                 if(j==m) break;

66                 if(min>a[j].dis-a[i].dis)

67                     min = a[j].dis - a[i].dis;

68             }

69             if(min == INF)

70                 printf("-1\n");

71             else

72                 printf("%d\n",min);

73         }

74     }

75     return 0;

76 }