HDU5469 Antonidas(树分治&&哈希)

#pragma warning(disable:4996)
#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <cmath>
#include <algorithm>
#include <string>
#include <cstdlib>
#include <ctime>
#include <map>
#include <set>
using namespace std;

#define maxn 10010
#define ll long long
#define MP make_pair

vector<int> G[maxn];
bool centroid[maxn];
int ssize[maxn];
char val[maxn];
char tar[maxn];
set<pair<ll, ll> > sta;
set<pair<ll, ll> >::iterator it;
int n, m;

ll mod_num;
ll mod;
ll xpow[maxn];
ll pre[maxn];
ll post[maxn];

ll xorr(ll x, ll y)
{
	return (x*mod_num%mod + y) % mod;
}

int compute_ssize(int v, int p)
{
	int c = 1;
	for (int i = 0; i<G[v].size(); ++i){
		int w = G[v][i];
		if (w == p || centroid[w]) continue;
		c += compute_ssize(G[v][i], v);
	}
	ssize[v] = c;
	return c;
}

pair<int, int> search_centroid(int v, int p, int t)
{
	pair<int, int> res = make_pair(INT_MAX, -1);
	int s = 1, m = 0;
	for (int i = 0; i < G[v].size(); ++i){
		int w = G[v][i];
		if (w == p || centroid[w]) continue;
		res = min(res, search_centroid(w, v, t));
		m = max(m, ssize[w]);
		s += ssize[w];
	}
	m = max(m, t - s);
	res = min(res, make_pair(m, v));
	return res;
}

void enumerate_mul(int v, int p, pair<ll, ll> d, set<pair<ll, ll> > &ds)
{
	if (!ds.count(d)) ds.insert(d);
	for (int i = 0; i < G[v].size(); ++i){
		int w = G[v][i];
		if (w == p || centroid[w]) continue;
		enumerate_mul(w, v, MP(d.first + 1, xorr(d.second, val[w])), ds);
	}
}

bool judge(pair<ll, ll> x, const set<pair<ll, ll> >& tds)
{
	if (pre[x.first] == x.second){
		return tds.count(MP(m - x.first, post[x.first + 1]));
	}
	if (post[m - x.first + 1] == x.second){
		return tds.count(MP(m - x.first, pre[m - x.first]));
	}
	return false;
}


bool solve(int v)
{
	compute_ssize(v, -1);
	int s = search_centroid(v, -1, ssize[v]).second;
	centroid[s] = true;
	for (int i = 0; i<G[s].size(); ++i){
		if (centroid[G[s][i]]) continue;
		if (ssize[G[s][i]] < m){
			continue;
		}
		if (solve(G[s][i])) {
			return true;
		}
	}
	sta.clear();
	sta.insert(MP(1, val[s]));
	if (m == 1 && val[s] == tar[1]){
		return true;
	}
	set<pair<ll, ll> > tds;
	for (int i = 0; i<G[s].size(); ++i){
		if (centroid[G[s][i]]) continue;
		tds.clear();
		enumerate_mul(G[s][i], s, MP(1, val[G[s][i]]), tds);
		it = tds.begin();
		while (it != tds.end()){
			if (judge(*it, sta)){
				return true;
			}
			++it;
		}
		it = tds.begin();
		while (it != tds.end()){
			ll one = (*it).first;
			ll two = (*it).second;
			pair<ll, ll> vv;
			if (one > m){
				++it; continue;
			}
			if (pre[one] != two && post[m - one + 1] != two){
				++it;
				continue;
			}
			if (tar[one + 1] != val[s] && tar[m - one] != val[s]){
				++it;
				continue;
			}
			vv.first = one + 1;
			vv.second = (xpow[one] * val[s] % mod + two) % mod;
			if (!sta.count(vv)){
				sta.insert(vv);
			}
			++it;
		}
	}
	centroid[s] = false;
	return false;
}

ll haha[3] = { 37, 23, 53 };
ll tata[2] = { 1000000007, 1000010009 };

int main()
{
	int T; cin >> T; int ca = 0;
	while (T--)
	{
		cin >> n;
		for (int i = 0; i <= n; ++i) G[i].clear();
		int ui, vi;
		for (int i = 0; i < n - 1; ++i){
			scanf("%d%d", &ui, &vi);
			G[ui].push_back(vi);
			G[vi].push_back(ui);
		}
		memset(centroid, 0, sizeof(centroid));
		scanf("%s", val + 1);
		scanf("%s", tar + 1);
		mod_num = haha[rand() % 3];
		mod = tata[rand() % 2];
		xpow[0] = 1;
		for (int i = 1; i <= n; ++i){
			xpow[i] = xpow[i - 1] * mod_num%mod;
		}
		pre[0] = 0;
		m = strlen(tar + 1);
		for (int i = 1; i <= m; ++i){
			pre[i] = (xpow[i - 1] * tar[i] % mod + pre[i - 1]) % mod;
		}
		post[m + 1] = 0;
		for (int i = m; i >= 1; --i){
			post[i] = (tar[i] * xpow[m - i] % mod + post[i + 1]) % mod;
		}
		bool flag = solve(1);
		if (flag){
			printf("Case #%d: Find\n", ++ca);
		}
		else{
			printf("Case #%d: Impossible\n", ++ca);
		}
	}
	return 0;
}