[BOJ/JAVA] 백준 16570번 : 앞뒤가 맞는 수열

16570번: 앞뒤가 맞는 수열

 

 

 

 

---

 

 

 

• 생각

 

 

KMP알고리즘으로 풀면 쉽게 풀 수 있을 것 같다.

 

 

 

 

• 코드

 

import java.io.IOException;
import java.io.InputStream;
import java.util.InputMismatchException;

public class Algorithm {
	static int[] array, pi;
	static int N;

	public static void main(String[] args) throws Exception {
		SetData();
	}

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

		N = in.nextInt();
		array = new int[N];
		pi = new int[N];

		for (int i = N - 1; i >= 0; i--) {
			array[i] = in.nextInt();
		}

		KMP();

		int length = 0, count = 0;
		for (int i = 0; i < N; i++) {
			if (pi[i] > length) {
				length = pi[i];
				count = 0;
			}
			if (pi[i] == length)
				count++;
		}
		if (length == 0)
			System.out.println("-1");
		else
			System.out.println(length + " " + count);
	}

	public static void KMP() {
		int j = 0;
		for (int i = 1; i < N; i++) {
			while (j > 0 && array[j] != array[i]) {
				j = pi[j - 1];
			}
			if (array[j] == array[i]) {
				pi[i] = ++j;
			}
		}
	}
}

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;
	}
}

 

 

 

• KMP 알고리즘이 아니여도 풀 수 있는 문제이다.

 

import java.io.IOException;
import java.io.InputStream;
import java.util.InputMismatchException;

public class Algorithm {
	static int[] array, pi;
	static int N;

	public static void main(String[] args) throws Exception {
		SetData();
	}

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

		N = in.nextInt();
		array = new int[N + 1];
		pi = new int[N + 1];

		for (int i = 1; i <= N; i++) {
			array[i] = in.nextInt();
		}

		KMP();

		for (int i = N; i >= 1; i--) {
			if (pi[i] != 0) {
				System.out.println(i + " " + pi[i]);
				System.exit(0);
			}
		}

		System.out.println(-1);
		
	}

	static void KMP() {
		for (int i = N - 1; i >= 1; i--) {
			int count = 0;
			int j = N;
			int index = i;
			while (array[index--] == array[j--]) {
				count++;
			}
			pi[count]++;
		}
	}
}

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;
	}
}