5. 중복 확인

import java.util.*;

class Main {
	public String solution(int N, int[] arr) {
		String answer = "";
		Set<Integer> set = new HashSet<>();
		for (int x : arr) {
			set.add(x);
		}
		if (set.size() != N)
			return "D";
		return "U";
	}

	public static void main(String[] args) {
		Main T = new Main();
		Scanner kb = new Scanner(System.in);
		int N = kb.nextInt();
		int[] arr = new int[N];
		for (int i = 0; i < N; i++)
			arr[i] = kb.nextInt();
		System.out.print(T.solution(N, arr));
		kb.close();
	}
}

 

import java.util.*;

class Main {
	public String solution(int N, int[] arr) {
		String answer = "";
		Map<Integer, Integer> map = new HashMap<>();
		for (int x : arr) {
			map.put(x, map.getOrDefault(x, 0) + 1);
			if (map.get(x) == 2)
				return "D";
		}
		return "U";
	}

	public static void main(String[] args) {
		Main T = new Main();
		Scanner kb = new Scanner(System.in);
		int N = kb.nextInt();
		int[] arr = new int[N];
		for (int i = 0; i < N; i++)
			arr[i] = kb.nextInt();
		System.out.print(T.solution(N, arr));
		kb.close();
	}
}

 

import java.util.*;

class Main {
	public String solution(int N, int[] arr) {
		String answer = "U";
		Arrays.sort(arr);
		for (int i = 0; i < N - 1; i++) {
			if (arr[i] == arr[i + 1]) {
				answer = "D";
				break;
			}
		}
		return answer;
	}

	public static void main(String[] args) {
		Main T = new Main();
		Scanner kb = new Scanner(System.in);
		int N = kb.nextInt();
		int[] arr = new int[N];
		for (int i = 0; i < N; i++)
			arr[i] = kb.nextInt();
		System.out.print(T.solution(N, arr));
		kb.close();
	}
}