[백준] 1389번 케빈 베이컨의 6단계 법칙 #JAVA

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.StringTokenizer;

public class Main {

    static final int INF = 987654321;

    public static void main(String[] args) throws NumberFormatException, IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st = new StringTokenizer(br.readLine()," ");

        int N = Integer.parseInt(st.nextToken());
        int M = Integer.parseInt(st.nextToken());
        int[][] arr = new int[N+1][N+1];
        for (int i = 1; i <= N; i++) {
            for (int j = 1; j <= N; j++) {
                if(i==j) continue;
                arr[i][j] = INF;
            }
        }

        for (int i = 0; i < M; i++) {
            st = new StringTokenizer(br.readLine()," ");
            int a = Integer.parseInt(st.nextToken());
            int b = Integer.parseInt(st.nextToken());

            arr[a][b] = arr[b][a] = 1;
        }

        for (int k = 1; k <= N; k++) {
            for (int i = 1; i <= N; i++) {
                for (int j = 1; j <= N; j++) {
                    // 단순히 갈 수 있는 경로가 있는지만 체크함.
                    if (arr[i][j] > arr[i][k] + arr[k][j]) {
                        arr[i][j] = arr[i][k] + arr[k][j];
                    }
                }
            }
        }
        int answer = 987654321;
        int idx = -1;
        for (int i = 1; i <= N; i++) {
            int tot = 0;
            for (int j = 1; j <= N; j++) {
                   tot += arr[i][j];
            }
            if(answer > tot){
                answer = tot;
                idx = i;
            }
        }
        bw.write(idx + "\n");
        bw.flush();
        bw.close();
        br.close();
    }
}