[20250218] BOJ / G4 / 키 순서 / 권혁준

khj20006/202502/18 BOJ G4 키 순서.md

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+### 플로이드
+
+```cpp
+
+#include <iostream>
+#include <vector>
+using namespace std;
+int main()
+{
+	int N, M;
+	cin >> N >> M;
+	vector<vector<bool>> D(N + 1, vector<bool>(N + 1));
+	for (int i = 1; i <= N; i++) D[i][i] = 1;
+	for (int i = 0, a, b; i < M; i++) {
+		cin >> a >> b;
+		D[a][b] = 1;
+	}
+
+	for (int i = 1; i <= N; i++) for (int j = 1; j <= N; j++) for (int k = 1; k <= N; k++) {
+		if (D[j][i] && D[i][k]) D[j][k] = 1;
+	}
+
+	int ans = 0;
+	for (int i = 1; i <= N; i++) {
+		int res = 0;
+		for (int j = 1; j <= N; j++) res += D[i][j] + D[j][i];
+		ans += res == N + 1;
+	}
+	cout << ans;
+
+}
+
+```
+
+### 위상 정렬
+
+```cpp
+
+#include <iostream>
+#include <vector>
+#include <queue>
+using namespace std;
+
+int main()
+{
+	int N, M;
+	cin >> N >> M;
+	vector<vector<int>> V(N + 1);
+	vector<vector<bool>> D(N + 1, vector<bool>(N + 1));
+	vector<int> in(N + 1);
+	for (int i = 1; i <= N; i++) D[i][i] = 1;
+	for (int i = 0, a, b; i < M; i++) {
+		cin >> a >> b;
+		V[a].push_back(b);
+		in[b]++;
+	}
+
+	queue<int> Q;
+	for (int i = 1; i <= N; i++) if (!in[i]) Q.push(i);
+
+	while (!Q.empty()) {
+		int x = Q.front();
+		Q.pop();
+		for (int i : V[x]) {
+			for (int j = 1; j <= N; j++) if (D[j][x]) D[j][i] = 1;
+			if (!(--in[i])) Q.push(i);
+		}
+	}
+
+	int ans = 0;
+	for (int i = 1; i <= N; i++) {
+		int res = 0;
+		for (int j = 1; j <= N; j++) res += D[i][j] + D[j][i];
+		ans += res == N + 1;
+	}
+	cout << ans;
+
+}
+
+```