hdu 2586 LCA

思路：裸的LCA

#include<map>

#include<set>

#include<cmath>

#include<queue>

#include<cstdio>

#include<vector>

#include<string>

#include<cstdlib>

#include<cstring>

#include<iostream>

#include<algorithm>

#define pb push_back

#define mp make_pair

#define Maxn 40010

#define Maxm 80002

#define LL __int64

#define Abs(x) ((x)>0?(x):(-x))

#define lson(x) (x<<1)

#define rson(x) (x<<1|1)

#define inf 0x7fffffff

#define Mod 1000000007

using namespace std;

int head[Maxn],vi[Maxn],e,fs[Maxn],fa[Maxn],anc[Maxn],vis[Maxn],dis[Maxn],ans[Maxn];

struct Edge{

    int u,v,next,val;

}edge[Maxm];

vector< pair<int,int> > que[Maxn];

void init()

{

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

    memset(vi,0,sizeof(vi));

    memset(vis,0,sizeof(vis));

    memset(fs,0,sizeof(fs));

    memset(dis,0,sizeof(dis));

    for(int i=0;i<Maxn;i++){

        fa[i]=i;

    }

    e=0;

}

void add(int u,int v,int val)

{

    edge[e].u=u,edge[e].v=v,edge[e].val=val,edge[e].next=head[u],head[u]=e++;

    edge[e].u=v,edge[e].v=u,edge[e].val=val,edge[e].next=head[v],head[v]=e++;

}

int find(int x)

{

    if(x!=fa[x])

        fa[x]=find(fa[x]);

    return fa[x];

}

void merg(int a,int b)

{

    int x=find(a);

    int y=find(b);

    if(fs[y]<=fs[x])

        fa[y]=x,fs[x]+=fs[y];

    else fa[x]=y,fs[y]+=fs[x];

}

void LCA(int u)

{

    int i,v,sz;

    sz=que[u].size();

    vi[u]=1;

    anc[u]=u;

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

        v=edge[i].v;

        if(vi[v]) continue;

        LCA(v);

        merg(u,v);

        anc[find(u)]=u;

    }

    vis[u]=1;

    for(i=0;i<sz;i++){

        v=que[u][i].first;

        if(vis[v]){

            int lca=anc[find(v)];

            int x=que[u][i].second;

            ans[x]=dis[u]+dis[v]-2*dis[lca];

        }

    }

}

void dfs(int u)

{

    int i,v;

    vi[u]=1;

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

        v=edge[i].v;

        if(vi[v]) continue;

        dis[v]=dis[u]+edge[i].val;

        dfs(v);

    }

}

int main()

{

    int t,n,m,i,j,u,v,val;

    scanf("%d",&t);

    while(t--){

        init();

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

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

            scanf("%d%d%d",&u,&v,&val);

            add(u,v,val);

        }

        for(i=1;i<=m;i++){

            scanf("%d%d",&u,&v);

            que[u].pb(mp(v,i));

            que[v].pb(mp(u,i));

        }

        dis[1]=0;

        dfs(1);

        memset(vi,0,sizeof(vi));

        LCA(1);

        for(i=1;i<=m;i++){

            printf("%d\n",ans[i]);

        }

    }

    return 0;

}