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: Accepted)

n = gets.to_s.to_i
@s = gets.to_s.chomp.bytes

@h = Hash.new{|h, k| h[k] = []}
@s.each.with_index(1){|c, i| @h[c] << i}
@s = @s.unshift(32)

def update(i, c)
  d = @s[i]
  return if c == d
  @s[i] = c
  @h[d].delete_at(@h[d].bsearch_index{|x| x >= i})
  @h[c].insert((@h[c].bsearch_index{|x| x >= i} || -1), i)
end

gets
readlines.each do |x|
    a, b, c = x.to_s.chomp.split
    b = b.to_i

    if a == '1'
        update(b, c.ord)
    else
        c = c.to_i
        puts @h.each_value.count {|e| (e.bsearch{|x| x >= b} or n+1) <= c}
    end
end