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_i
S = gets.chomp
Q = gets
Qs = readlines.map(&:split)

@h = Hash.new{|h, k| h[k] = []}
@s = "_" + S.dup
S.each_char.with_index(1){|c, i| @h[c] << i}

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

def _kind?(c, l, r)
  (@h[c].bsearch{|x| x >= l} || N + 1) < (@h[c].bsearch{|x| x > r} || N + 1)
end

def kind(l, r)
  ('a' .. 'z').count{|c| _kind?(c, l, r)}
end

Qs.each do |a, b, c|
  if a == '1'
    update(b.to_i, c)
  else
    puts kind(b.to_i, c.to_i)
  end
end