Merge pull request #160 from AlgorithmWithGod/03do-new30

[20250220] BOJ / G4 / 키 순서 / 신동윤

Author: ShinHeeEul

03do-new30/202502/20 BOJ G4 키 순서.md

@@ -0,0 +1,62 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    final static int INF = 501;
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        // [start] 입출력
+        int N = Integer.parseInt(st.nextToken()); // 정점의 개수
+        int M = Integer.parseInt(st.nextToken()); // 엣지의 개수
+
+        int[][] dist = new int[N+1][N+1];
+        for (int i = 0; i < N+1; i++) {
+            for (int j = 0; j < N+1; j++) {
+                if (i == j) { dist[i][j] = 0; continue;} // 자기 자신으로 가는 비용 0
+                dist[i][j] = INF; // 초기값: 도달할 수 없음으로 설정
+            }
+        }
+        for (int i = 0; i < M; i++) {
+            st = new StringTokenizer(br.readLine());
+            int u = Integer.parseInt(st.nextToken());
+            int v = Integer.parseInt(st.nextToken());
+            dist[u][v] = 1;
+        }
+        // [end] 입출력
+
+        // Floyd-Warshall
+        for (int mid = 1; mid < N+1; mid++) {
+            for (int start = 1; start < N+1; start++) {
+                for (int end = 1; end < N+1; end++) {
+                    dist[start][end] = Integer.min(dist[start][end], dist[start][mid] + dist[mid][end]);
+                }
+            }
+        }
+        int answer = 0;
+        for (int target = 1; target < N+1; target++) {
+            int lower = 0;
+            int higher = 0;
+            for (int k = 1; k < N+1; k++) {
+                if (target == k) { continue; } // 자기 자신과의 경로는 패스
+                if (dist[k][target] != INF) {
+                    lower++;
+                }
+                if (dist[target][k] != INF) {
+                    higher++;
+                }
+            }
+            if (lower + higher == N-1) {
+                answer++;
+            }
+        }
+        System.out.println(answer);
+
+        br.close();
+    }
+}
+
+```