백준 13023번: ABCDE [백트래킹][탐색][DFS] -Java

https://www.acmicpc.net/problem/13023

13023번: ABCDE

 

역시나 문제 이해하는데에 많은 시간을 소비..

결론은 5명이 연결된 친구관계가 있느냐(1) 없느냐(0)를 판단하는 것

 

 

<Java 코드>

package algorithm.boj;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.StringTokenizer;

public class Boj13023 {

	public static int N, M, ans =0;
	public static ArrayList<Integer> friend[];
	public static boolean visit[][], check[];
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub

		System.setIn(new FileInputStream("Test.txt"));
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		
		N = Integer.parseInt(st.nextToken());
		M = Integer.parseInt(st.nextToken());
		
		visit = new boolean[N][N];
		check = new boolean[N];
		friend = new ArrayList[N];
		
		for (int i = 0; i < N; i++) {
			friend[i] = new ArrayList<Integer>();
		}
		
		for (int i = 0; i < M; i++) {
			st = new StringTokenizer(br.readLine());
			int a = Integer.parseInt(st.nextToken());
			int b = Integer.parseInt(st.nextToken());
			
			friend[a].add(b);
			friend[b].add(a);
		}
		
		
		for (int i = 0; i < N; i++) {
			if(ans==1)
				break;
			check[i]=true;
			fun(i,0);
			check[i]=false;
		}
		
		System.out.println(ans);
		
	}
	
	public static void fun(int num, int cnt) {
		if(cnt == 4) {
			ans = 1;
			return;
		}
		
		for (int i = 0; i < friend[num].size(); i++) {
			int target = friend[num].get(i);
			
			if(visit[num][target] || visit[target][num]) //지나간 경로인가?
				continue;
			
			if(check[target]) //이미 한번 연결한 친구인가?
				continue;
			
			check[target] =true;
			visit[num][target] = visit[target][num] = true;
			fun(target,cnt+1);
			check[target] =false;
			visit[num][target] = visit[target][num] = false;
		}
	}

}