✅ graphs, matrix exponiation

submissions/ICPC/Maratona de Programação da SBC 2014/F. Teletransporte.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+using ll = long long;
+using vll = vector<ll>;
+using vll2d = vector<vll>;
+
+const int MAXN(100);
+const ll MOD(1'0'000);
+ll N, L, S, T;
+vll2d ways(MAXN, vll(MAXN));
+
+
+vll2d prod(vll2d &a, vll2d &b) {
+	vll2d c(N, vll(N, 0));
+
+	for (int i = 0; i < N; i++) {
+		for (int j = 0; j < N; j++) {
+			for (int k = 0; k < N; k++) {
+				c[i][j] = (c[i][j] + a[i][k] * b[k][j]) % MOD;
+			}
+		}
+	}
+
+	return c;
+}
+
+vll2d pow (vll2d &a, ll p) {
+	vll2d res(N, vll(N));
+
+	for (int i = 0; i < N; i++) {
+		res[i][i] = 1;
+	}
+
+	while (p) {
+		if (p&1) res = prod(res, a);
+		a = prod(a,a);
+		p >>= 1;
+	}
+
+	return res;
+}
+
+
+void solve() {
+
+	for (int i = 0; i < N; i++) {
+		for (int j = 0; j < N; j++) {
+			ways[i][j] = 0;
+		}
+	}
+
+	cin >> S >> T;
+
+	for (int i = 0; i < N; i++) {
+		for (int j = 0; j < 4; j++) {
+			int k;
+			cin >> k;
+			k--;
+			ways[i][k]++;
+		}
+	}
+
+	auto w2 = pow(ways, L);
+	cout << w2[S-1][T-1] << '\n';
+
+}
+
+int main() {
+	ios_base::sync_with_stdio(false);
+	cin.tie(0);
+	cout.tie(0);
+
+	while (cin >> N >> L) {
+		solve();
+	}
+
+}
+
+/*
+ * AC
+ * https://www.beecrowd.com.br/judge/pt/problems/view/1713
+ * Graphs
+ * Matrix Exponiation
+ * */