HDU2586 LCA

题意：给定n个点，n-1条边，每两个点之间的路独一无二

LCA

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 1 #include<stdio.h>

 2 #include<string.h>

 3 #include<stdlib.h>

 4 const int maxn = 40005;

 5 int head[ maxn ],cnt;

 6 struct node{

 7     int u,val,next;

 8 }edge[ maxn*2 ];

 9 int ace[ maxn ],fa[ maxn ],dis[ maxn ],deep[ maxn ];

10 void init(){

11     cnt=0;

12     memset( head,-1,sizeof( head ));

13     memset( fa,0,sizeof( fa ));

14 }

15 void addedge( int a,int b ,int c ){

16     edge[ cnt ].u=b;

17     edge[ cnt ].val=c;

18     edge[ cnt ].next=head[ a ];

19     head[ a ]=cnt++;

20 }

21 int n;

22 

23 void dfs( int now,int now_father,int now_deep,int now_dis,int now_ace ){

24     fa[ now ]=now_father;

25     deep[ now ]=now_deep;

26     dis[ now ]=now_dis;

27     deep[ now ]=now_deep;

28     for( int i=head[ now ];i!=-1;i=edge[ i ].next ){

29         int v=edge[ i ].u;

30         if( fa[ v ]==0 )

31             dfs( v,now,now_deep+1,now_dis+edge[ i ].val,now_ace );

32     }

33 }

34 

35 int find( int a,int b ){

36     if( a==b )

37         return a;

38     if( deep[ a ]>deep[ b ] )

39         return find( fa[ a ],b );

40     else 

41         return find( a,fa[ b ] );

42 }

43 

44 int main(){

45     int T;

46     scanf("%d",&T);

47     while( T-- ){

48         init();

49         int m;

50         scanf("%d%d",&n,&m);

51         int a,b,c;

52         for( int i=0;i<n-1;i++ ){

53             scanf("%d%d%d",&a,&b,&c);

54             addedge( a,b,c );

55             addedge( b,a,c );

56         }

57 

58         for( int i=1;i<=n;i++ )

59             if( fa[ i ]==0 )

60                 dfs( i,-1,0,1,i );//x,fa[x],deep,dis,ace

61 

62         while( m-- ){

63             scanf("%d%d",&a,&b);

64             if( ace[ a ]==ace[ b ] ){

65                 int k=find( a,b );

66                 printf("%d\n",dis[a]+dis[b]-2*dis[k]);

67             }

68             else

69                 printf("0\n");

70         }

71     //    printf("\n");

72     }

73     return 0;

74 }