백준 30804번(Java)

import java.io.*;
import java.util.*;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int N = Integer.parseInt(br.readLine());
		int[] fruits = new int[N];

		StringTokenizer st = new StringTokenizer(br.readLine());
		for (int i = 0; i < N; i++) {
			fruits[i] = Integer.parseInt(st.nextToken());
		}

		HashMap<Integer, Integer> fruitsCnt = new HashMap<>();
		int maxLength = 0;
		int left = 0;

		for (int right = 0; right < N; right++) {
			fruitsCnt.put(fruits[right], fruitsCnt.getOrDefault(fruits[right], 0) + 1);

			while (fruitsCnt.size() > 2) {
				fruitsCnt.put(fruits[left], fruitsCnt.get(fruits[left]) - 1);

				if (fruitsCnt.get(fruits[left]) == 0) {
					fruitsCnt.remove(fruits[left]);
				}

				left++;
			}
			maxLength = Math.max(maxLength, right - left + 1);
		}
		System.out.println(maxLength);
	}
}