結果

問題 No.1612 I hate Construct a Palindrome
コンテスト
ユーザー heno239
提出日時 2021-07-21 22:08:05
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
AC  
実行時間 102 ms / 2,000 ms
コード長 5,090 bytes
コンパイル時間 2,078 ms
コンパイル使用メモリ 170,140 KB
最終ジャッジ日時 2025-01-23 04:16:10
ジャッジサーバーID
（参考情報） 		judge3 / judge2
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ファイルパターン 結果
sample AC * 3
other AC * 36
権限があれば一括ダウンロードができます

ソースコード

diff # 

#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
#include<array>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
constexpr ll mod = 998244353;
const ll INF = mod * mod;
typedef pair<int, int>P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acosl(-1.0);

ll mod_pow(ll x, ll n, ll m = mod) {
	if (n < 0) {
		ll res = mod_pow(x, -n, m);
		return mod_pow(res, m - 2, m);
	}
	if (abs(x) >= m)x %= m;
	if (x < 0)x += m;
	ll res = 1;
	while (n) {
		if (n & 1)res = res * x % m;
		x = x * x % m; n >>= 1;
	}
	return res;
}
struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n % mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint& a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint& a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint& a, modint b) { a.n = ((ll)a.n * b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, ll n) {
	if (n == 0)return modint(1);
	modint res = (a * a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }
modint operator/=(modint& a, modint b) { a = a / b; return a; }
const int max_n = 1 << 18;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}
modint combP(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[a - b];
}

struct edge {
	int to, id;
};
void solve() {
	int n, m; cin >> n >> m;
	vector<int> a(m), b(m);
	vector<char> c(m);
	rep(i, m) {
		cin >> a[i] >> b[i] >> c[i]; a[i]--; b[i]--;
	}
	vector<vector<edge>> G(n);
	rep(i, m) {
		G[a[i]].push_back({ b[i],i });
		G[b[i]].push_back({ a[i],i });
	}
	vector<P> pres(n), pret(n);
	queue<int> q;
	vector<bool> used(n);
	used[0] = true;
	q.push(0);
	while (!q.empty()) {
		int id = q.front(); q.pop();
		for (edge e : G[id])if (!used[e.to]) {
			used[e.to] = true;
			pres[e.to] = { id,e.id };
			q.push(e.to);
		}
	}
	fill(all(used), false);
	q.push(n-1); used[n - 1] = true;
	while (!q.empty()) {
		int id = q.front(); q.pop();
		for (edge e : G[id])if (!used[e.to]) {
			used[e.to] = true;
			pret[e.to] = { id,e.id };
			q.push(e.to);
		}
	}
	auto find_road = [&](int fr, int to) {
		if (fr == 0) {
			vector<int> res;
			int cur = to;
			while (cur > 0) {
				P p = pres[cur];
				res.push_back(p.second);
				cur = p.first;
			}
			reverse(all(res));
			return res;
		}
		else {
			//to=n-1
			vector<int> res;
			int cur = fr;
			while (cur < n - 1) {
				P p = pret[cur];
				res.push_back(p.second);
				cur = p.first;
			}
			return res;
		}
	};
	auto ispp = [&](vector<int> v)->bool {
		int len = v.size();
		rep(i, len / 2) {
			if (c[v[i]] != c[v[len - 1 - i]])return false;
		}
		return true;
	};
	vector<int> r = find_road(0, n - 1);
	if (!ispp(r)) {
		cout << r.size()<<"\n"; rep(i, r.size())cout << r[i] + 1 << "\n"; return;
	}
	char z = c[r[0]];
	int memo = r[0];
	int chk = -1;
	rep(i, m)if (c[i] != z) {
		chk = i;
	}
	if (chk < 0) {
		cout << -1 << "\n"; return;
	}
	r = find_road(0, a[chk]);
	vector<int> r2 = find_road(b[chk], n - 1);
	r.push_back(chk);
	rep(i, r2.size())r.push_back(r2[i]);
	if (!ispp(r)) {
		cout << r.size() << "\n"; rep(i, r.size())cout << r[i] + 1 << "\n"; return;
	}
	rep(aa, 2)r.insert(r.begin(), memo);
	cout << r.size() << "\n"; rep(i, r.size())cout << r[i] + 1 << "\n"; return;

}

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(12);
	//init_f();
	//init();
	//expr();
	//int t; cin >> t; rep(i, t)
	solve();
	return 0;
}
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