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

View Code 
 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 }

 

posted @ 2013-02-05 20:06  xxx0624  阅读(375)  评论(0)  编辑  收藏  举报