Problem:
Set: Range Search

For a set $S$ of integers, perform a sequence of the following operations. Note that each value in $S$ must be unique.

insert($x$): Insert $x$ to $S$ and report the number of elements in $S$ after the operation.

find($x$): Report the number of $x$ in $S$ (0 or 1).

delete($x$): Delete $x$ from $S$.

dump($L$, $R$): Print elements $x$ in $S$ such that $L \leq x \leq R$.

Input

The input is given in the following format.

$q$
$query_1$
$query_2$
:
$query_q$

Each query $query_i$ is given by

0 $x$

or

1 $x$

or

2 $x$

or

3 $L$ $R$

where the first digits 0, 1, 2 and 3 represent insert, find, delete and dump operations respectively.

Output

For each insert operation, print the number of elements in $S$.

For each find operation, print the number of specified elements in $S$.

For each dump operation, print the corresponding elements in ascending order. Print an element in a line.

Constraints

$1 \leq q \leq 200,000$

$0 \leq x \leq 1,000,000,000$

The total number of elements printed by dump operations does not exceed $1,000,000$

Sample Input 1

9
0 1
0 2
0 3
2 2
1 1
1 2
1 3
0 4
3 2 4

Sample Output 1

1
2
3
1
0
1
3
3
4

Solution in C# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using SB = System.Text.StringBuilder;
//using System.Text.RegularExpressions;
//using System.Globalization;
//using System.Diagnostics;
using static System.Console;
using System.Numerics;
using static System.Math;
using pair = Pair<int, int>;

class Program
{
    static void Main()
    {
        SetOut(new StreamWriter(OpenStandardOutput()) { AutoFlush = false });
        new Program().solve();
        Out.Flush();
    }
    readonly Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 }; //→↓←↑
    readonly int mod = 1000000007;
    readonly int dom = 998244353;
    bool chmax<T>(ref T a, T b) where T : IComparable<T> { if (a.CompareTo(b) < 0) { a = b; return true; } return false; }
    bool chmin<T>(ref T a, T b) where T : IComparable<T> { if (b.CompareTo(a) < 0) { a = b; return true; } return false; }

    void solve()
    {
        int Q = cin.nextint;
        var S = new MultiSet<int>();
        for (int i = 0; i < Q; i++)
        {
            int mode = cin.nextint;
            if (mode == 0)
            {
                S.Add(cin.nextint);
                WriteLine(S.Count);
            }
            else if (mode == 1)
            {
                WriteLine(S[cin.nextint]);
            }
            else if (mode == 2)
            {
                S.Remove(cin.nextint);
            }
            else
            {
                S.GetViewBetween(cin.nextint, cin.nextint);
            }
        }

    }

}

class MultiSet<T> : SortedList<T, int> where T : IComparable<T>
{
    readonly bool is_multi;
    public MultiSet(bool is_multi = false)
    {
        this.is_multi = is_multi;
    }
    public void Add(T item)
    {
        if (is_multi || this[item] == 0)
        {
            Count++;
            this[item]++;
        }
    }
    public new void Remove(T item)
    {
        int size;
        if (TryGetValue(item, out size))
        {
            Count -= size;
            base.Remove(item);
        }
    }
    public void GetViewBetween(T lowerValue, T upperValue)
    {
        var s = Keys.lower_bound(lowerValue);
        var t = Keys.upper_bound(upperValue);
        for (int i = s; i < t; i++)
        {
            for (int j = 0; j < Values[i]; j++)
            {
                WriteLine(Keys[i]);
            }
        }
    }
    public new int this[T key]
    {
        get
        {
            int value;
            return TryGetValue(key, out value) ? value : 0;
        }
        set
        {
            base[key] = value;
        }
    }
    public new int Count { get; private set; }
}

static class Ex
{
    public static void join<T>(this IEnumerable<T> values, string sep = " ") => WriteLine(string.Join(sep, values));
    public static string concat<T>(this IEnumerable<T> values) => string.Concat(values);
    public static string reverse(this string s) { var t = s.ToCharArray(); Array.Reverse(t); return t.concat(); }

    public static int lower_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) < 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
    public static int upper_bound<T>(this IList<T> arr, T val) where T : IComparable<T>
    {
        int low = 0, high = arr.Count;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >> 1) + low;
            if (arr[mid].CompareTo(val) <= 0) low = mid + 1;
            else high = mid;
        }
        return low;
    }
}

class Pair<T, U> : IComparable<Pair<T, U>> where T : IComparable<T> where U : IComparable<U>
{
    public T f; public U s;
    public Pair(T f, U s) { this.f = f; this.s = s; }
    public int CompareTo(Pair<T, U> a) => f.CompareTo(a.f) != 0 ? f.CompareTo(a.f) : s.CompareTo(a.s);
    public override string ToString() => $"{f} {s}";
}

class Scanner
{
    string[] s; int i;
    readonly char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan => ReadLine().Split();
    public int[] scanint => Array.ConvertAll(scan, int.Parse);
    public long[] scanlong => Array.ConvertAll(scan, long.Parse);
    public double[] scandouble => Array.ConvertAll(scan, double.Parse);
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint => int.Parse(next);
    public long nextlong => long.Parse(next);
    public double nextdouble => double.Parse(next);
}