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: Time Limit Exceeded)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Text;
using System.Linq;

using E = System.Linq.Enumerable;

internal partial class Solver {
    public void Run() {
        var n = ni();
        var q = ni();
        var c = ni(n).Select(x => x - 1).ToArray();
        var l = new int[q];
        var r = new int[q];
        for (int i = 0; i < q; i++) {
            l[i] = ni() - 1;
            r[i] = ni() - 1;
        }
        var count = new int[n];
        var distinctNum = 0;
        var mo = new AnonymousMo<int>(n,
            add: i => { if (count[c[i]]++ == 0) distinctNum++; },
            remove: i => { if (--count[c[i]] == 0) distinctNum--; },
            result: () => distinctNum
        );
        for (int i = 0; i < q; i++) {
            mo.AddQuery(l[i], r[i] + 1);
        }
        var ans = mo.ProcessAll();
        cout.WriteLine(ans.JoinToString("\n"));
    }
}

/// <summary>
/// Mo's algorithm
/// </summary>
public abstract class Mo<TResult> {
    private readonly int _blockSize;
    private int _start = 0, _end = 0, queryIndex = 0;
    private readonly List<Query> query = new List<Query>();

    private struct Query {
        public int Left, Right, Id;
    }

    protected Mo(int size) {
        _blockSize = (int)Math.Sqrt(size);
    }

    public void AddQuery(int l, int r) { // [l, r)
        int id = query.Count;
        query.Add(new Query { Left = l, Right = r, Id = id });
    }

    public void Build() {
        query.Sort((q1, q2) =>
            (q1.Left / _blockSize == q2.Left / _blockSize)
                ? q1.Left.CompareTo(q2.Left)
                : (q1.Right.CompareTo(q2.Right) * (q1.Left / _blockSize % 2 == 1 ? 1 : -1))
        );
        _start = _end = queryIndex = 0;
    }

    public int Process() {
        var q = query[queryIndex++];
        while (q.Left < _start) {
            Add(--_start);
        }
        while (_end < q.Right) {
            Add(_end++);
        }
        while (_start < q.Left) {
            Remove(_start++);
        }
        while (q.Right < _end) {
            Remove(--_end);
        }
        return q.Id;
    }

    public TResult[] ProcessAll() {
        var result = new TResult[query.Count];
        for (int _ = 0; _ < query.Count; _++) {
            var id = Process();
            result[id] = GetResult();
        }
        return result;
    }

    protected abstract void Add(int index);
    protected abstract void Remove(int index);
    public abstract TResult GetResult();
}

public class AnonymousMo<TResult> : Mo<TResult> {
    private readonly Action<int> _addMethod, _removeMethod;
    private readonly Func<TResult> _resultMethod;
    public AnonymousMo(int size, Action<int> add, Action<int> remove, Func<TResult> result) : base(size) {
        _addMethod = add;
        _removeMethod = remove;
        _resultMethod = result;
    }

    protected override void Add(int index) {
        _addMethod(index);
    }

    protected override void Remove(int index) {
        _removeMethod(index);
    }

    public override TResult GetResult() {
        return _resultMethod();
    }
}
// PREWRITEN CODE BEGINS FROM HERE

static public class StringExtensions {
    static public string JoinToString<T>(this IEnumerable<T> source, string separator = " ") {
        return string.Join(separator, source);
    }
}

internal partial class Solver : Scanner {
    public static void Main() {
#if LOCAL
        byte[] inputBuffer = new byte[1000000];
        var inputStream = Console.OpenStandardInput(inputBuffer.Length);
        using (var reader = new StreamReader(inputStream, Console.InputEncoding, false, inputBuffer.Length)) {
            Console.SetIn(reader);
            new Solver(Console.In, Console.Out).Run();
        }
#else
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        new Solver(Console.In, Console.Out).Run();
        Console.Out.Flush();
#endif
    }

#pragma warning disable IDE0052
    private readonly TextReader cin;
    private readonly TextWriter cout;
    private readonly TextWriter cerr;
#pragma warning restore IDE0052

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        cin = reader;
        cout = writer;
        cerr = Console.Error;
    }

    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

#pragma warning disable IDE1006
#pragma warning disable IDE0051
    private int ni() { return NextInt(); }
    private int[] ni(int n) { return NextIntArray(n); }
    private long nl() { return NextLong(); }
    private long[] nl(int n) { return NextLongArray(n); }
    private double nd() { return NextDouble(); }
    private double[] nd(int n) { return NextDoubleArray(n); }
    private string ns() { return Next(); }
    private string[] ns(int n) { return NextArray(n); }
#pragma warning restore IDE1006
#pragma warning restore IDE0051
}

#if DEBUG
internal static class LinqPadExtension {
    public static string TextDump<T>(this T obj) {
        if (obj is IEnumerable) return (obj as IEnumerable).Cast<object>().JoinToString().Dump();
        else return obj.ToString().Dump();
    }
    public static T Dump<T>(this T obj) {
        return LINQPad.Extensions.Dump(obj);
    }
}
#endif

public class Scanner {
    private readonly TextReader Reader;
    private readonly CultureInfo ci = CultureInfo.InvariantCulture;

    private readonly char[] buffer = new char[2 * 1024];
    private int cursor = 0, length = 0;
    private string Token;
    private readonly StringBuilder sb = new StringBuilder(1024);

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        Reader = reader;
    }

    public int NextInt() { return checked((int)NextLong()); }
    public long NextLong() {
        var s = Next();
        long r = 0;
        int i = 0;
        bool negative = false;
        if (s[i] == '-') {
            negative = true;
            i++;
        }
        for (; i < s.Length; i++) {
            r = r * 10 + (s[i] - '0');
#if DEBUG
            if (!char.IsDigit(s[i])) throw new FormatException();
#endif
        }
        return negative ? -r : r;
    }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        string[] array = new string[size];
        for (int i = 0; i < size; i++) {
            array[i] = Next();
        }

        return array;
    }
    public int[] NextIntArray(int size) {
        int[] array = new int[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextInt();
        }

        return array;
    }

    public long[] NextLongArray(int size) {
        long[] array = new long[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextLong();
        }

        return array;
    }

    public double[] NextDoubleArray(int size) {
        double[] array = new double[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextDouble();
        }

        return array;
    }

    public string Next() {
        if (Token == null) {
            if (!StockToken()) {
                throw new Exception();
            }
        }
        var token = Token;
        Token = null;
        return token;
    }

    public bool HasNext() {
        if (Token != null) {
            return true;
        }

        return StockToken();
    }

    private bool StockToken() {
        while (true) {
            sb.Clear();
            while (true) {
                if (cursor >= length) {
                    cursor = 0;
                    if ((length = Reader.Read(buffer, 0, buffer.Length)) <= 0) {
                        break;
                    }
                }
                var c = buffer[cursor++];
                if (33 <= c && c <= 126) {
                    sb.Append(c);
                } else {
                    if (sb.Length > 0) break;
                }
            }

            if (sb.Length > 0) {
                Token = sb.ToString();
                return true;
            }

            return false;
        }
    }
}