240627 List of Unique Numbers

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

	int n = Integer.parseInt(br.readLine().trim());
	StringTokenizer st = new StringTokenizer(br.readLine().trim());

	int[] lastPosition = new int[100001];
	long sum = 0;
	int start = 0;

	for (int i = 1; i <= n; i++) {
		int num = Integer.parseInt(st.nextToken());

		if (start < lastPosition[num]) {
			start = lastPosition[num];
		}

		lastPosition[num] = i;
		sum += (i - start);
	}
	System.out.println(sum);
}

출처:https://www.acmicpc.net/problem/13144