Subway (树中心 + 树hash)

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

const int mod = 1e9 + 7;
const int maxn = 1e5 + 12345;
const int seed = 17;
char inp[16], onp[16];

struct Tree{
    map<string, int>id;
    vector<int>edge[maxn];
    string anw[maxn], rip[maxn];
    int _cnt, ctr[2], siz[maxn], dep[maxn], fa[maxn];
    LL Har[maxn];
    
    ///将遍历顺序存进去
    void done(int st, int fa){
        if(fa == 0) _cnt = 0;
        anw[_cnt ++] = rip[st];
        for(auto x : edge[st]){
            if(x == fa) continue;
            done(x, st);
        }
    }

    ///hash技术
    LL dfsh(int st, int fa){
        Har[st] = seed;siz[st] = 1;
        for(auto x : edge[st]){
            if(x == fa) continue;
            dfsh(x, st);
            siz[st] += siz[x];
        }
        sort(edge[st].begin(), edge[st].end(),
            [&](int x, int y){return Har[x] < Har[y];});
        for(auto x : edge[st]){
            if(x == fa) continue;
            Har[st] = (((Har[st] * Har[x]) % mod) ^ Har[x])% mod;
        }
        Har[st] = (Har[st] + siz[st]) % mod;
        Har[st] = (Har[st] * Har[st]) % mod;
        return Har[st];
    }

    ///得到深度值
    void getdep(int st, int Fa, int Dep){
        dep[st] = Dep;fa[st] = Fa;
        for(auto x : edge[st]){
            if(x == fa[st]) continue;
            getdep(x,st,Dep + 1);
        }
    }

    ///获取中点
    void getCtr(int n){
        getdep(1, 0, 0);
        ctr[0] = max_element(dep + 1, dep + 1 + n) - dep;
        getdep(ctr[0], 0, 0);
        ctr[0] = max_element(dep + 1, dep + 1 + n) - dep;
        int fdep = dep[ctr[0]];
        for(int i = 0; i < fdep/2; i ++)
            ctr[0] = fa[ctr[0]];
        ctr[1] = ctr[0];
        if(fdep & 1) ctr[1] = fa[ctr[1]];
    }

    ///重置数据
    void init(int n){
        for(int i = 0; i <= n; i ++)
            edge[i].clear();
        id.clear();_cnt = 1;
    }

    ///映射连接的符号,并存进对应的map值为下标的地方
    int toid(string v){
        if(id.find(v) != id.end()) return id[v];
        rip[_cnt] = v;
        return id[v] = _cnt ++;
    }

    ///建图，映射值
    void input(int n){
        init(n);int l,r;
        for(int i = 1; i < n; i ++){
            scanf("%s %s", inp, onp);
            l = toid(inp); r = toid(onp);
            edge[l].push_back(r);
            edge[r].push_back(l);
        }
    }
}X, Y;

void solve(){
    for(int i = 0; i < 2; i ++)
    for(int j = 0; j < 2; j ++)
    if(X.dfsh(X.ctr[i], 0) == Y.dfsh(Y.ctr[j], 0)){
        X.done(X.ctr[i], 0);
        Y.done(Y.ctr[j], 0);
        return;
    }
}

int main(){
    int n;while(~scanf("%d", &n)){
        X.input(n);
        Y.input(n);
        X.getCtr(n);
        Y.getCtr(n);
        solve();
        for(int i = 0; i < n; i ++)
            printf("%s %s\n",X.anw[i].c_str(), Y.anw[i].c_str());
    }return 0;
}