HDU 5732 Subway（2016多校1J，树的重心 + 哈希）

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)
#define dec(i, a, b)	for (int i(a); i >= (b); --i)

typedef unsigned long long LL;

const LL  A = 90918567;
const LL  B = 87378051;
const LL  mod  = 1e9 + 7;
const int N = 1e5 + 10;

int a[N], ans[N], father[N], roota[3], rootb[3];
int numa, numb, n, x, y, c1, c2, L, R, cnt;
bool flag;
map <string, int> mp1, mp2;
vector <int> v[N], g[N];
string ss[N], tt[N], s1, s2;
LL  c[N], f[N];

void init(){
	mp1.clear();
	mp2.clear();
	rep(i, 0, n + 1) v[i].clear(), g[i].clear();
	c1 = 0, c2 = 0;
}

int get1(string s){
	if (mp1.count(s)) return mp1[s];
	mp1[s] = ++c1;
	ss[c1] = s;
	return c1;
}

int get2(string s){
	if (mp2.count(s)) return mp2[s];
	mp2[s] = ++c2;
	tt[c2] = s;
	return c2;
}

void dfs1(int x, int fa, int now, vector <int> v[N]){
	if (now > c1){
		c1 = now;
		L = x;
	}

	for (auto u : v[x]){
		if (u == fa) continue;
		dfs1(u, x, now + 1, v);
	}
}

void dfs2(int x, int fa, int now, vector <int> v[N]){
	father[x] = fa;
	if (now > c2){
		c2 = now;
		R = x;
	}

	for (auto u : v[x]){
		if (u == fa) continue;
		dfs2(u, x, now + 1, v);
	}
}

void gethash_a(int x, int fa){
	vector <LL> val;
	for (auto u : v[x]){
		if (u == fa) continue;
		gethash_a(u, x);
		val.push_back(c[u]);
	}

	sort(val.begin(), val.end());
	c[x] = B;
	for (auto u : val){
		c[x] = (c[x] * A ^ u) % mod;
	}
}

void gethash_b(int x, int fa){
	vector <LL> val;
	for (auto u : g[x]){
		if (u == fa) continue;
		gethash_b(u, x);
		val.push_back(f[u]);
	}

	sort(val.begin(), val.end());
	
	f[x] = B;
	for (auto u : val){
		f[x] = (f[x] * A ^ u) % mod;
	}
}

bool cmp_a(const int &a, const int &b){
	return c[a] < c[b];
}

bool cmp_b(const int &a, const int &b){
	return f[a] < f[b];
}

void work(int x, int y, int fa_a, int fa_b){
	vector <int> na, nb;
	for (auto u : v[x]) if (u != fa_a) na.push_back(u);
	for (auto u : g[y]) if (u != fa_b) nb.push_back(u);

	if ((int)na.size() != (int)nb.size()){
		return;
	}

	sort(na.begin(), na.end(), cmp_a);
	sort(nb.begin(), nb.end(), cmp_b);

	int sz = (int)na.size();

	rep(i, 0, sz - 1) if (c[na[i]] == f[nb[i]]) ans[na[i]] = nb[i];


	rep(i, 0, sz - 1){
		int u1 = na[i], u2 = nb[i];
		work(u1, u2, x, y);
	}
}

bool solve(int roota, int rootb){
	gethash_a(roota, 0);
	gethash_b(rootb, 0);

	memset(ans, -1, sizeof ans);

	if (c[roota] != f[rootb]) return false;

	ans[roota] = rootb;
	work(roota, rootb, 0, 0);

	bool ret = true;
	rep(i, 1, n) if (ans[i] == -1){
		ret = false;
		break;
	}

	return ret;
}

void print(){
	rep(i, 1, n) cout << ss[i] << " " << tt[ans[i]] << endl;
}

int main(){

	ios::sync_with_stdio(false);

	while (cin >> n){

		init();
		rep(i, 2, n){
			cin >> s1 >> s2;
			x = get1(s1);
			y = get1(s2);
			v[x].push_back(y);
			v[y].push_back(x);
		}

		rep(i, 2, n){
			cin >> s1 >> s2;
			x = get2(s1);
			y = get2(s2);
			g[x].push_back(y);
			g[y].push_back(x);
		}

		L = 0, R = 0;
		c1 = 0, c2 = 0;
		dfs1(1, 0, 0, v);
		memset(father, 0, sizeof father);
		dfs2(L, 0, 0, v);

		x = R;
		cnt = 0;
		numa = 0;
		while (true){
			a[++cnt] = R;
			R = father[R];
			if (R == 0) break;
		}

		if (cnt & 1) roota[++numa] = a[(cnt + 1) / 2];

		else{
			roota[++numa] = a[cnt / 2];
			roota[++numa] = a[cnt / 2 + 1];
		}

		L = 0, R = 0;
		c1 = 0, c2 = 0;
		dfs1(1, 0, 0, g);
		memset(father, 0, sizeof father);
		dfs2(L, 0, 0, g);

		x = R;
		cnt = 0;
		numb = 0;
		while (true){
			a[++cnt] = R;
			R = father[R];
			if (R == 0) break;
		}

		if (cnt & 1) rootb[++numb] = a[(cnt + 1) / 2];

		else{
			rootb[++numb] = a[cnt / 2];
			rootb[++numb] = a[cnt / 2 + 1];
		}

		flag = false;
		rep(i, 1, numa){
			rep(j, 1, numb){
				if (solve(roota[i], rootb[j])){
					flag = true;
					print();
					break;
				}
			}
			if (flag) break;
		}
	}

	return 0;
}