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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;
import java.math.*;
import java.awt.Point;
 
public class Main {
	//static final long MOD = 998244353L;
	//static final long INF = -1000000000000000007L;
	static final long MOD = 1000000007L;
	//static final int INF = 1000000007;
	
	//static long[] factorial;
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		String s = sc.next();
		SegmentTree[] trees = new SegmentTree[26];
		int[] pos = new int[N];
		for (int i = 0; i < 26; i++)
			trees[i] = new SegmentTree(N);
		for (int i = 0; i < N; i++) {
			int c = s.charAt(i)-'a';
			trees[c].update(0, 0, N-1, i, 1);
			pos[i] = c;
		}
		int Q = sc.ni();
		for (int q = 0; q < Q; q++) {
			int t = sc.ni();
			if (t == 1) {
				//update
				int ind = sc.ni()-1;
				int c = (sc.next().charAt(0)-'a');
				trees[pos[ind]].update(0, 0, N-1, ind, 0);
				trees[c].update(0, 0, N-1, ind, 1);
				pos[ind] = c;
			} else {
				//query
				int L = sc.ni()-1;
				int R = sc.ni()-1;
				int ans = 0;
				for (int i = 0; i < 26; i++) {
					if (trees[i].query(0, 0, N-1, L, R) > 0) {
						ans++;
					}
				}
				pw.println(ans);
			}
		}
		pw.close();
	}
	
	//No lazy propagation. 0 indexed. Very fast.
	static class SegmentTree {
		public long[] arr;
		public long[] tree;

		//Zero initialization
		public SegmentTree(int N) {
			arr = new long[N];
			tree = new long[4*N+1];
		}

		public long query(int treeIndex, int lo, int hi, int i, int j) {
			// query for arr[i..j]
			if (lo > j || hi < i)
				return 0;
			if (i <= lo && j >= hi)
				return tree[treeIndex];
			int mid = lo + (hi - lo) / 2;

			if (i > mid)
				return query(2 * treeIndex + 2, mid + 1, hi, i, j);
			else if (j <= mid)
				return query(2 * treeIndex + 1, lo, mid, i, j);

			long leftQuery = query(2 * treeIndex + 1, lo, mid, i, mid);
			long rightQuery = query(2 * treeIndex + 2, mid + 1, hi, mid + 1, j);

			// merge query results
			return merge(leftQuery, rightQuery);
		}

		public void update(int treeIndex, int lo, int hi, int arrIndex, long val) {
			if (lo == hi) {
				tree[treeIndex] = val;
				arr[arrIndex] = val;
				return;
			}

			int mid = lo + (hi - lo) / 2;

			if (arrIndex > mid)
				update(2 * treeIndex + 2, mid + 1, hi, arrIndex, val);
			else if (arrIndex <= mid)
				update(2 * treeIndex + 1, lo, mid, arrIndex, val);

			// merge updates
			tree[treeIndex] = merge(tree[2 * treeIndex + 1], tree[2 * treeIndex + 2]);
		}

		public long merge(long a, long b) {
			return (a+b);
		}
	}
	
	public static long dist(long[] p1, long[] p2) {
		return (Math.abs(p2[0]-p1[0])+Math.abs(p2[1]-p1[1]));
	}
	
	//Find the GCD of two numbers
	public static long gcd(long a, long b) {
		if (a < b) return gcd(b,a);
		if (b == 0)
			return a;
		else
			return gcd(b,a%b);
	}
	
	//Fast exponentiation (x^y mod m)
	public static long power(long x, long y, long m) { 
		if (y < 0) return 0L;
		long ans = 1;
		x %= m;
		while (y > 0) { 
			if(y % 2 == 1) 
				ans = (ans * x) % m; 
			y /= 2;  
			x = (x * x) % m;
		} 
		return ans; 
	}
	
	public static int[][] shuffle(int[][] array) {
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		return array;
	}
	
    public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
 
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] a, int[] b) {
				  //return a[0]-b[0]; //ascending order
				  if (a[0] != b[0]) {
					  return (a[0]-b[0]);
				  } else {
					  return (a[1]-b[1]);
				  }
	          }
		});
		return array;
	}
    
    public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
        	  public int compare(long[] a, long[] b) {
				  if (a[0] < b[0])
					  return -1;
				  else
					  return 1;
	          }
		});
		return array;
	}
    
    static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    }
}