[최단경로] 2171024 신수정

13_최단 경로/필수/2458..cpp

@@ -0,0 +1,49 @@
+// 2458
+// 플로이드-워셜 알고리즘 이용
+
+#include <iostream>
+#include <algorithm>
+#include <vector>
+
+using namespace std;
+const int CONNECT = 1;
+
+void floydWarShall(int N, vector<vector<int>> &adj){
+    for(int i = 1; i <= N; i++){
+        for(int j = 1; j <= N; j++){
+            for(int k = 1; k <= N; k++){
+                if(adj[j][i] && adj[i][k]) {
+                    adj[j][k] = CONNECT;
+                }
+            }
+        }
+    }
+}
+
+int main(){
+    ios_base::sync_with_stdio(false); cin.tie(0);
+    int N, M, x, y;
+    cin >> N >> M;
+    vector<vector<int>> adj(N+1, vector<int>(N+1, 0));
+    while(M--){
+        cin >> x >> y;
+        adj[x][y] = CONNECT;
+    }
+    floydWarShall(N, adj);
+    // 답 얻어내기
+    int answer = 0;
+    for(int i = 1; i <= N; i++){
+        int connected_student = 0;
+        for(int j = 1; j <= N; j++) {
+            if(adj[i][j] == CONNECT || adj[j][i] == CONNECT) {
+                connected_student++; // 자신을 제외한 N-1명 학생이 연결돼있나?
+
+                if(connected_student >= N-1) { // N-1명 이상이 연결되어있음
+                    answer++;
+                }
+            }
+        }
+    }
+    cout << answer << "\n";
+
+}