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 }