Week9 김명진 2617 구슬 찾기 풀이

src/week9/findBead1103/Main.java

@@ -1,4 +1,80 @@
 package week9.findBead1103;
 
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.*;
+
+// 	14280	152
 public class Main {
+    static int N, M;
+    static ArrayList<Integer>[] forwardAdjList;
+    static ArrayList<Integer>[] backwardAdjList;
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        M = Integer.parseInt(st.nextToken());
+        forwardAdjList = new ArrayList[N + 1]; // 나보다 큰친구들을 찾는 adjList
+        backwardAdjList = new ArrayList[N + 1]; // 나보다 작은 친구들을 찾는 adjList
+        for (int vertex = 1; vertex <= N; vertex++) {
+            forwardAdjList[vertex] = new ArrayList<>();
+            backwardAdjList[vertex] = new ArrayList<>();
+        }
+        for (int edge = 0; edge < M; edge++) {
+            st = new StringTokenizer(br.readLine());
+            int from = Integer.parseInt(st.nextToken());
+            int to = Integer.parseInt(st.nextToken());
+            forwardAdjList[from].add(to);
+            backwardAdjList[to].add(from);
+        }
+
+        int[] forwardMap = new int[N+1];
+        int[] backwardMap = new int[N+1];
+
+        for (int startNode = 1; startNode <= N; startNode++) {
+            int forwardRes = bfs(forwardAdjList, startNode);
+            int backwardRes = bfs(backwardAdjList, startNode);
+            forwardMap[startNode] = forwardRes;
+            backwardMap[startNode] = backwardRes;
+        }
+        int count = 0;
+        for(int forwardCount : forwardMap){
+            // 큰사람들 중에서 전체 절반보다 큰사람이 많이 알고 있다면
+            if(forwardCount > N/2)count++;
+        }
+        for(int backward : backwardMap){
+            // 작은 중에서 전체 절반보다 큰사람이 많이 알고 있다면
+            if(backward > N/2)count++;
+        }
+        System.out.println(count);
+    }
+
+    private static int bfs(ArrayList<Integer>[] adjList, int startNode) {
+        Queue<Integer> q = new ArrayDeque<>();
+        boolean[] check = new boolean[N + 1];
+        q.add(startNode);
+        check[startNode] = true;
+        while (!q.isEmpty()){
+            int curNode = q.poll();
+            ArrayList<Integer> nextNodeList = adjList[curNode];
+            for (Integer nextNode : nextNodeList){
+                if(!check[nextNode]){
+                    check[nextNode] = true;
+                    q.offer(nextNode);
+                }
+            }
+        }
+        int count = 0;
+        // 탐색한 친구들 갯수 count
+        for(boolean el : check){
+            if(el)count++;
+        }
+        // 자기자신은 뺀다
+        return count-1;
+    }
+
+
 }