Problem:
Score : 600 points

Problem Statement

We have N colored balls arranged in a row from left to right; the color of the i-th ball from the left is c_i.

You are given Q queries. The i-th query is as follows: how many different colors do the l_i-th through r_i-th balls from the left have?

Constraints

1\leq N,Q \leq 5 \times 10^5

1\leq c_i \leq N

1\leq l_i \leq r_i \leq N

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N Q
c_1 c_2 \cdots c_N
l_1 r_1
l_2 r_2
:
l_Q r_Q

Output

Print Q lines. The i-th line should contain the response to the i-th query.

Sample Input 1

4 3
1 2 1 3
1 3
2 4
3 3

Sample Output 1

2
3
1

The 1-st, 2-nd, and 3-rd balls from the left have the colors 1, 2, and 1 - two different colors.

The 2-st, 3-rd, and 4-th balls from the left have the colors 2, 1, and 3 - three different colors.

The 3-rd ball from the left has the color 1 - just one color.

Sample Input 2

10 10
2 5 6 5 2 1 7 9 7 2
5 5
2 4
6 7
2 2
7 8
7 9
1 8
6 9
8 10
6 8

Sample Output 2

1
2
2
1
2
2
6
3
3
3

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using static System.Console;
using static System.Math;
using static MyIO;
using static MyUtil;

public class F { public static void Main() => (new Solver()).Solve(); }

public class Solver
{
	public void Solve()
	{
		long N = GetLong();
		long Q = GetLong();
		var c = GetLongs(N);
		var queries = Range(0, N).Select(_ => new List<(long, long)>()).ToArray();
		for(long i = 0; i < Q; i++)
		{
			long l = GetLong() - 1;
			long r = GetLong() - 1;
			queries[r].Add((i, l));
		}

		var pos = Enumerable.Repeat(-1L, (int)N + 1).ToArray();
		var st = new SegmentTree<long>(N, 0, (x, y) => x + y);
		var ans = new long[Q];
		for(long r = 0; r < N; r++)
		{
			if(pos[c[r]] != -1)
				st.Update(pos[c[r]], 0);

			pos[c[r]] = r;
			st.Update(r, 1);

			foreach(var (i, l) in queries[r])
				ans[i] = st.Query(l, r + 1);
		}

		WriteLine(string.Join("\n", ans));
	}
}

public class SegmentTree<T>
{
	private long N;
	private T INI;
	private Func<T, T, T> Func;
	private T[] dat;

	public T this[long index]
	{
		get { return dat[index + N - 1]; }
		set { Update(index, value); }
	}

	public SegmentTree(long n, T ini, Func<T, T, T> func)
	{
		N = 1;		
		while(N < n)
			N <<= 1;

		INI = ini;
		Func = func;
			
		dat = new T[2 * N - 1];
		for(long i = 0; i < 2 * N - 1; i++)
			dat[i] = INI;
	}

	public void Update(long k, T a)
	{
		k += N - 1;
		dat[k] = a;
		while(k > 0)
		{
			k = (k - 1) / 2;
			dat[k] = Func(dat[k * 2 + 1], dat[k * 2 + 2]);
		}
	}

	public T Query(long a, long b, long k = 0, long l = 0, long r = -1)
	{
		if(r == -1)
			r = N;

		if(r <= a || b <= l)
			return INI;

		if(a <= l && r <= b)
			return dat[k];
		else
		{
			T vl = Query(a, b, k * 2 + 1, l, (l + r) / 2);
			T vr = Query(a, b, k * 2 + 2, (l + r) / 2, r);
			return Func(vl, vr);
		}
	}
}

public static class MyIO
{
	private static string[] args = new string[0];
	private static int cnt = 0;
	private static IEnumerable<string> getArgs(long N) => Range(0, N).Select(_ => getArg());
	private static string getArg()
	{
		if(cnt == args.Length) { args = Console.ReadLine().Split(); cnt = 0; }
		return args[cnt++];
	}

	public static int GetInt() => int.Parse(getArg());
	public static long GetLong() => long.Parse(getArg());
	public static double GetDouble() => double.Parse(getArg());
	public static decimal GetDecimal() => decimal.Parse(getArg());
	public static string GetString() => getArg();
	public static char GetChar() => getArg()[0];
	public static int[] GetInts(long N) => getArgs(N).Select(int.Parse).ToArray();
	public static long[] GetLongs(long N) => getArgs(N).Select(long.Parse).ToArray();
	public static double[] GetDoubles(long N) => getArgs(N).Select(double.Parse).ToArray();
	public static decimal[] GetDecimals(long N) => getArgs(N).Select(decimal.Parse).ToArray();
	public static string[] GetStrings(long N) => getArgs(N).ToArray();
}

public static class MyUtil
{
	public static void chmax<T>(ref T x, T y) where T : IComparable<T> { if(x.CompareTo(y) < 0) x = y; }
	public static void chmin<T>(ref T x, T y) where T : IComparable<T> { if(x.CompareTo(y) > 0)	x = y; }
	public static void swap<T>(ref T x, ref T y) { T tmp = x; x = y; y = tmp; }
	public static long rightShift(long x, long y) => (x >> (int)y);
	public static long leftShift(long x, long y) => (x << (int)y);
	public static bool contains(long s, long x) => (rightShift(s, x) & 1L) == 1L;
	public static long gcd(long x, long y) => (y == 0) ? x : gcd(y, x % y);
	public static long lcm(long x, long y) => (x / gcd(x,y)) * y;	
	public static IEnumerable<int> Range(long start, long count) => Enumerable.Range((int)start, (int)count);
	public static void Sort(this List<string> source) => source.Sort(StringComparer.Ordinal);
}