[BOJ/JAVA] 백준 2617번 : 구슬 찾기

2617번: 구슬 찾기

 

 

 

 

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• 풀이

 

 

highDown 배열에 dfs방식을 통해 자신보다 높은 수, 적은 수의 개수를 저장해주었다.

자신보다 낮은수 or 높은수가 (N+1)/2 보다 높으면 중간 구슬이 될 수 없기때문에 answer을 +1해주었다.

 

 

 

• 코드

 

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.InputMismatchException;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;

public class Main {
	static int N, M, answer;
	static ArrayList<Integer>[] array;
	static int[][] highDown;
	static boolean[] check;

	public static void main(String[] args) throws Exception {
		SetData();
		System.out.println(answer);
	}

	// 데이터
	private static void SetData() throws Exception {
		InputReader in = new InputReader(System.in);

		N = in.nextInt();
		M = in.nextInt();
		answer = 0;
		array = new ArrayList[N+1];
		highDown = new int[N+1][2];
		
		for(int i = 1; i <= N; i++) {
			array[i] = new ArrayList<>();
		}
		
		for(int i = 1; i <= M; i++) {
			array[in.nextInt()].add(in.nextInt());
		}
		
		for(int i = 1; i <= N; i++) {
			check = new boolean[N+1];
			dfs(i, i);
		}
		
		for(int i = 1; i <= N; i++) {
			if(highDown[i][0] >= (N+1)/2 || highDown[i][1] >= (N+1)/2)
				answer++;
		}
	}
	
	private static void dfs(int index, int current) {
		check[current] = true;
		for(int i = 0 ; i < array[current].size(); i++) {
			int next = array[current].get(i);
			if(check[next]) continue;
			
			highDown[index][0]++;
			highDown[next][1]++;
			dfs(index, next);
		}
	}
}

class InputReader {
	private final InputStream stream;
	private final byte[] buf = new byte[8192];
	private int curChar, snumChars;

	public InputReader(InputStream st) {
		this.stream = st;
	}

	public int read() {
		if (snumChars == -1)
			throw new InputMismatchException();
		if (curChar >= snumChars) {
			curChar = 0;
			try {
				snumChars = stream.read(buf);
			} catch (IOException e) {
				throw new InputMismatchException();
			}
			if (snumChars <= 0)
				return -1;
		}
		return buf[curChar++];
	}

	public int nextInt() {
		int c = read();
		while (isSpaceChar(c)) {
			c = read();
		}
		int sgn = 1;
		if (c == '-') {
			sgn = -1;
			c = read();
		}
		int res = 0;
		do {
			res *= 10;
			res += c - '0';
			c = read();
		} while (!isSpaceChar(c));
		return res * sgn;
	}

	public long nextLong() {
		int c = read();
		while (isSpaceChar(c)) {
			c = read();
		}
		int sgn = 1;
		if (c == '-') {
			sgn = -1;
			c = read();
		}
		long res = 0;
		do {
			res *= 10;
			res += c - '0';
			c = read();
		} while (!isSpaceChar(c));
		return res * sgn;
	}

	public int[] nextIntArray(int n) {
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = nextInt();
		}
		return a;
	}

	public String nextLine() {
		int c = read();
		while (isSpaceChar(c))
			c = read();
		StringBuilder res = new StringBuilder();
		do {
			res.appendCodePoint(c);
			c = read();
		} while (!isEndOfLine(c));
		return res.toString();
	}

	public boolean isSpaceChar(int c) {
		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
	}

	private boolean isEndOfLine(int c) {
		return c == '\n' || c == '\r' || c == -1;
	}
}