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 Ruby (2.3.3) (judge verdict: Wrong Answer)

#require 'pp'
require 'set'

n = gets.to_i
s = gets.chomp!.codepoints

a_p = 97

memo = Array.new(26)
0.upto(25).each do |i|
    memo[i] = SortedSet.new
end
s.each.with_index(1) do |ch, i|
    memo[ch - a_p] << i
end

#pp s
#pp memo

q = gets.to_i
q.times do |i|
    query = gets.split
    if query[0] == '1'
        i_q, c_q = query[1].to_i, query[2] 
        current_point = s[i_q-1] - a_p
        new_point = c_q.codepoints[0] - a_p
        next if current_point == new_point
           
        memo[current_point].delete(i_q-1)
        memo[new_point] << (i_q-1)
    else
        l_q, r_q = query[1].to_i, query[2].to_i
        count = 0
        
        0.upto(25) do |i|
            tmp = memo[i].to_a
            lower = tmp.bsearch {|x| x >= l_q }
            if lower == nil
                upper = tmp.bsearch{|x| x >= r_q }
                if upper
                    count += 1
                end
            elsif lower <= r_q
                count += 1
            end
        end

        puts count
    end
end