Problem:
Score : 500 points

Problem Statement

You are given a string S of length N consisting of lowercase English letters.

Process Q queries of the following two types:

Type 1: change the i_q-th character of S to c_q. (Do nothing if the i_q-th character is already c_q.)

Type 2: answer the number of different characters occurring in the substring of S between the l_q-th and r_q-th characters (inclusive).

Constraints

N, Q, i_q, l_q, and r_q are integers.

S is a string consisting of lowercase English letters.

c_q is a lowercase English letter.

1 \leq N \leq 500000

1 \leq Q \leq 20000

|S| = N

1 \leq i_q \leq N

1 \leq l_q \leq r_q \leq N

There is at least one query of type 2 in each testcase.

Input

Input is given from Standard Input in the following format:

N
S
Q
Query_1
\vdots
Query_Q

Here, Query_i in the 4-th through (Q+3)-th lines is one of the following:

1 i_q c_q

2 l_q r_q

Output

For each query of type 2, print a line containing the answer.

Sample Input 1

7
abcdbbd
6
2 3 6
1 5 z
2 1 1
1 4 a
1 7 d
2 1 7

Sample Output 1

3
1
5

In the first query, cdbb contains three kinds of letters: b , c , and d, so we print 3.

In the second query, S is modified to abcdzbd.

In the third query, a contains one kind of letter: a, so we print 1.

In the fourth query, S is modified to abcazbd.

In the fifth query, S does not change and is still abcazbd.

In the sixth query, abcazbd contains five kinds of letters: a, b, c, d, and z, so we print 5.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;

namespace AtCoder
{
	public class Program
	{
		static void Main()
		{
			var cin = new Scanner();
			int n = cin.Int();
			string s = cin.Next();
			int q = cin.Int();
			char[] ss = s.Select(x => (char)(x - 'a')).ToArray();

			var segs = new LazySegmentTree<int>[26];
			for (int i = 0; i < 26; i++) {
				segs[i] = new LazySegmentTree<int>(n + 1, 0, (x, y) => x + y);
			}

			for (int i = 0; i < n; i++) {
				var c = s[i] - 'a';
				segs[c].Update(i + 1, n + 1, 1);
			}

			var sb = new StringBuilder();
			for (int i = 0; i < q; i++) {
				int qq = cin.Int();
				if (qq == 1) {
					int ii = cin.Int() - 1;
					char c = (char)(cin.Next()[0] - 'a');
					if (ss[ii] != c) {
						int c2 = ss[ii];
						ss[ii] = c;
						segs[c2].Update(ii + 1, n + 1, -1);
						segs[c].Update(ii + 1, n + 1, 1);
					}
				} else {
					int l = cin.Int() - 1;
					int r = cin.Int();
					int cnt = 0;
					for (int j = 0; j < 26; j++) {
						if (segs[j].Query(r) - segs[j].Query(l) > 0) {
							cnt++;
						}
					}

					sb.AppendLine(cnt.ToString());
				}
			}

			Console.WriteLine(sb.ToString());
		}
	}

	public class LazySegmentTree<T>
	{
		private readonly int n_;
		private readonly int height_;
		private readonly T unit_;
		private readonly T[] tree_;
		private readonly bool[] should_;
		private readonly Func<T, T, T> merge_;

		public int Count { get; }

		public LazySegmentTree(int count, T unit, Func<T, T, T> merge)
		{
			merge_ = merge;
			unit_ = unit;

			Count = count;
			n_ = 1;
			height_ = 0;
			while (n_ < count) {
				n_ <<= 1;
				++height_;
			}

			tree_ = new T[n_ << 1];
			should_ = new bool[n_ << 1];
			for (int i = 0; i < tree_.Length; i++) {
				tree_[i] = unit;
			}
		}

		public LazySegmentTree(IReadOnlyList<T> src, T unit, Func<T, T, T> merge)
			: this(src.Count, unit, merge)
		{
			for (int i = 0; i < src.Count; i++) {
				tree_[i] = src[i];
			}
		}

		public T this[int i]
		{
			get { return Query(i); }
		}

		public T Query(int i)
		{
			int l = 0;
			int r = n_;
			int k = 1;
			while (r - l > 1) {
				Evaluate(k);
				int m = (l + r) / 2;
				if (i < m) {
					r = m;
					k = k << 1;
				} else {
					l = m;
					k = (k << 1) + 1;
				}
			}

			return tree_[k];
		}

		public void Update(int left, int right, T item)
		{
			if (left > right || right < 0 || left >= Count) {
				return;
			}

			int l = left + n_;
			int r = right + n_;
			Determine(l);
			Determine(r - 1);
			while (l < r) {
				if ((l & 1) != 0) {
					tree_[l] = merge_(tree_[l], item);
					should_[l] = true;
					++l;
				}

				if ((r & 1) != 0) {
					--r;
					tree_[r] = merge_(tree_[r], item);
					should_[r] = true;
				}

				l >>= 1;
				r >>= 1;
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private void Determine(int k)
		{
			for (int i = height_; i > 0; i--) {
				Evaluate(k >> i);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private void Evaluate(int k)
		{
			if (should_[k]) {
				if (k < n_) {
					tree_[k << 1] = merge_(tree_[k << 1], tree_[k]);
					should_[k << 1] = true;
					tree_[(k << 1) + 1] = merge_(tree_[(k << 1) + 1], tree_[k]);
					should_[(k << 1) + 1] = true;
					tree_[k] = unit_;
				}

				should_[k] = false;
			}
		}
	}

	public struct ModInt
	{
		public static long P { get; set; } = (long)1e9 + 7;

		public static ModInt Pow(ModInt value, long k)
		{
			return Pow(value.Value, k);
		}

		public static ModInt Pow(long value, long k)
		{
			long ret = 1;
			for (k %= P - 1; k > 0; k >>= 1, value = value * value % P) {
				if ((k & 1) == 1) {
					ret = ret * value % P;
				}
			}
			return new ModInt(ret);
		}

		public static ModInt Inverse(ModInt value)
		{
			return Pow(value, P - 2);
		}

		public long Value;

		public ModInt(long value)
		{
			value %= P;
			if (value < 0) {
				value += P;
			}

			Value = value;
		}

		public static ModInt operator +(ModInt lhs, ModInt rhs)
		{
			lhs.Value += rhs.Value;
			if (lhs.Value >= P) {
				lhs.Value -= P;
			}
			return lhs;
		}

		public static ModInt operator -(ModInt lhs, ModInt rhs)
		{
			lhs.Value -= rhs.Value;
			if (lhs.Value < 0) {
				lhs.Value += P;
			}

			return lhs;
		}

		public static ModInt operator *(ModInt lhs, ModInt rhs)
		{
			return new ModInt(lhs.Value * rhs.Value % P);
		}
		public static ModInt operator /(ModInt lhs, ModInt rhs)
		{
			long exp = P - 2;
			while (exp > 0) {
				if (exp % 2 > 0) {
					lhs *= rhs;
				}

				rhs *= rhs;
				exp /= 2;
			}

			return lhs;
		}

		public static implicit operator ModInt(long n)
		{
			n %= P;
			if (n < 0) {
				n += P;
			}

			return new ModInt(n);
		}

		public override string ToString()
		{
			return Value.ToString();
		}
	}

	public class HashMap<TKey, TValue> : Dictionary<TKey, TValue>
	{
		private readonly Func<TKey, TValue> initialzier_;
		public HashMap(Func<TKey, TValue> initialzier)
			: base()
		{
			initialzier_ = initialzier;
		}

		public HashMap(Func<TKey, TValue> initialzier, int capacity)
			: base(capacity)
		{
			initialzier_ = initialzier;
		}

		new public TValue this[TKey key]
		{
			get
			{
				if (ContainsKey(key) == false) {
					base[key] = initialzier_(key);
				}

				return base[key];
			}

			set { base[key] = value; }
		}
	}

	public static class Helper
	{
		public static void UpdateMin<T>(ref T target, T value) where T : IComparable<T>
			=> target = target.CompareTo(value) > 0 ? value : target;

		public static void UpdateMin<T>(ref T target, T value, Action<T> onUpdated) where T : IComparable<T>
		{
			if (target.CompareTo(value) > 0) {
				target = value;
				onUpdated(value);
			}
		}

		public static void UpdateMax<T>(ref T target, T value) where T : IComparable<T>
			=> target = target.CompareTo(value) < 0 ? value : target;
		public static void UpdateMax<T>(ref T target, T value, Action<T> onUpdated) where T : IComparable<T>
		{
			if (target.CompareTo(value) < 0) {
				target = value;
				onUpdated(value);
			}
		}

		public static T[] Array<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToArray();
		public static List<T> List<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToList();
		public static T[,] Array2<T>(int n, int m, T init)
		{
			var array = new T[n, m];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					array[i, j] = init;
				}
			}

			return array;
		}

		public static T[,] Array2<T>(int n, int m, Func<int, int, T> initializer)
		{
			var array = new T[n, m];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					array[i, j] = initializer(i, j);
				}
			}

			return array;
		}

		public static T[,,] Array3<T>(int n1, int n2, int n3, T init)
		{
			var array = new T[n1, n2, n3];
			for (int i1 = 0; i1 < n1; i1++) {
				for (int i2 = 0; i2 < n2; i2++) {
					for (int i3 = 0; i3 < n3; i3++) {
						array[i1, i2, i3] = init;
					}
				}
			}

			return array;
		}

		private static readonly int[] delta4_ = { 1, 0, -1, 0, 1 };
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void DoAt4(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int dn = 0; dn < 4; dn++) {
				int d4i = i + delta4_[dn];
				int d4j = j + delta4_[dn + 1];
				if ((uint)d4i < (uint)imax && (uint)d4j < (uint)jmax) {
					action(d4i, d4j);
				}
			}
		}

		private static readonly int[] delta8_ = { 1, 0, -1, 0, 1, 1, -1, -1, 1 };
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void DoAt8(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int dn = 0; dn < 8; dn++) {
				int d8i = i + delta8_[dn];
				int d8j = j + delta8_[dn + 1];
				if ((uint)d8i < (uint)imax && (uint)d8j < (uint)jmax) {
					action(d8i, d8j);
				}
			}
		}
	}

	public class Scanner
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private readonly Func<string> reader_;
		private string[] buf_;
		private int index_;

		public Scanner(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		public string NextLine() => reader_();
		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		public int Int() => int.Parse(Next());
		public long Long() => long.Parse(Next());
		public double Double() => double.Parse(Next());

		public int[] ArrayInt(int N, int add = 0)
		{
			int[] Array = new int[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Int() + add;
			}
			return Array;
		}

		public long[] ArrayLong(int N, long add = 0)
		{
			long[] Array = new long[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Long() + add;
			}
			return Array;
		}

		public double[] ArrayDouble(int N, double add = 0)
		{
			double[] Array = new double[N];
			for (int i = 0; i < N; i++) {
				Array[i] = Double() + add;
			}
			return Array;
		}

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}