A Research on "The Hundred Family Surnames" HihoCoder - 1387

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#include <bits/stdc++.h>
using namespace std;

struct node1
{
    int v;
    int next;
};

struct node2
{
    int x;
    int y;
    int dis;
};

map <string,int> mp;
node1 edge[200010];
node2 pre[100010];
int dp[100010][20];
int first[100010],clr[100010],deep[100010];
int n,q,num;

void addedge(int u,int v)
{
    edge[num].v=v;
    edge[num].next=first[u];
    first[u]=num++;
    return;
}

void dfs(int cur,int fa)
{
    int i,v;
    for(i=first[cur];i!=-1;i=edge[i].next)
    {
        v=edge[i].v;
        if(v!=fa)
        {
            dp[v][0]=cur;
            deep[v]=deep[cur]+1;
            dfs(v,cur);
        }
    }
    return;
}

void solve()
{
    int i,j;
    dp[1][0]=0;
    deep[1]=1;
    dfs(1,0);
    for(j=1;(1<<j)<=n;j++)
    {
        for(i=1;i<=n;i++)
        {
            dp[i][j]=dp[dp[i][j-1]][j-1];
        }
    }
    return;
}

int getlca(int u,int v)
{
    int i;
    if(deep[u]<deep[v]) swap(u,v);
    for(i=log2(n);i>=0;i--)
    {
        if(deep[dp[u][i]]>=deep[v])
        {
            u=dp[u][i];
        }
    }
    if(u==v) return u;
    for(i=log2(n);i>=0;i--)
    {
        if(dp[u][i]!=dp[v][i])
        {
            u=dp[u][i];
            v=dp[v][i];
        }
    }
    return dp[u][0];
}

int main()
{
    string s1,s2;
    int i,u,v,lca,cnt,ans;
    int lca1,lca2;
    while(scanf("%d%d",&n,&q)!=EOF)
    {
        mp.clear();
        cnt=0;
        for(i=1;i<=n;i++)
        {
            cin>>s1;
            if(mp[s1]==0) mp[s1]=++cnt;
            clr[i]=mp[s1];
        }
        memset(first,-1,sizeof(first));
        num=0;
        for(i=1;i<=n-1;i++)
        {
            scanf("%d%d",&u,&v);
            addedge(u,v);
            addedge(v,u);
        }
        solve();
        memset(pre,-1,sizeof(pre));
        for(i=1;i<=n;i++)
        {
            if(pre[clr[i]].x==-1) pre[clr[i]].x=i,pre[clr[i]].y=i,pre[clr[i]].dis=0;
            else if(pre[clr[i]].x==pre[clr[i]].y)
            {
                pre[clr[i]].y=i;
                lca=getlca(pre[clr[i]].x,pre[clr[i]].y);
                pre[clr[i]].dis=deep[pre[clr[i]].x]+deep[pre[clr[i]].y]-2*deep[lca];
            }
            else
            {
                lca1=getlca(i,pre[clr[i]].x);
                lca2=getlca(i,pre[clr[i]].y);
                if(pre[clr[i]].dis<max(deep[i]+deep[pre[clr[i]].x]-2*deep[lca1],deep[i]+deep[pre[clr[i]].y]-2*deep[lca2]))
                {
                    if(deep[i]+deep[pre[clr[i]].x]-2*deep[lca1]>deep[i]+deep[pre[clr[i]].y]-2*deep[lca2])
                    {
                        pre[clr[i]].y=i;
                        pre[clr[i]].dis=deep[i]+deep[pre[clr[i]].x]-2*deep[lca1];
                    }
                    else
                    {
                        pre[clr[i]].x=i;
                        pre[clr[i]].dis=deep[i]+deep[pre[clr[i]].y]-2*deep[lca2];
                    }
                }

            }
        }
        //printf("***%d***\n",cnt);
        //for(i=1;i<=cnt;i++) printf("*%d %d %d*\n",pre[i].x,pre[i].y,pre[i].dis);
        while(q--)
        {
            cin>>s1>>s2;
            u=mp[s1],v=mp[s2];
            if(u==0||v==0) printf("-1\n");
            else if(u==v) printf("%d\n",pre[u].dis+1);
            else
            {
                //printf("***%d %d %d %d***\n",u,v,pre[v].x,pre[v].y);
                //ans=max(pre[u].dis,pre[v].dis);
                ans=0;
                lca=getlca(pre[u].x,pre[v].x);
                ans=max(ans,deep[pre[u].x]+deep[pre[v].x]-2*deep[lca]);
                lca=getlca(pre[u].x,pre[v].y);
                ans=max(ans,deep[pre[u].x]+deep[pre[v].y]-2*deep[lca]);
                lca=getlca(pre[u].y,pre[v].x);
                ans=max(ans,deep[pre[u].y]+deep[pre[v].x]-2*deep[lca]);
                lca=getlca(pre[u].y,pre[v].y);
                ans=max(ans,deep[pre[u].y]+deep[pre[v].y]-2*deep[lca]);
                printf("%d\n",ans+1);
            }
        }
    }
    return 0;
}