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.chars
Q = gets.to_i
qu = []
Q.times{
  qu << gets.chomp.split(" ")
}

s = Hash.new{|h, k| h[k] = []}
(0...N).each{|i|
  s[S[i]] << (i+1)
}

qu.each{|f, a, b|
  if f == '1' then
    a_i = a.to_i
    if S[a_i-1] != b then
      idx = s[S[a_i-1]].bsearch_index{|x| x >= a_i}
      s[S[a_i-1]].delete_at(idx)
      S[a_i-1] = b
      idx = s[b].bsearch_index{|x| x >= a_i}
      idx.nil? ? s[b] << a_i : s[b].insert(idx, a_i)
    end
  else
    l, r = [a.to_i, b.to_i]
    ans = 0
    (0..25).each{|i|
      sl = s[(97+i).chr].bsearch{|x| x >= l}
      ans += 1 if (not sl.nil?) && sl <= r
    }
    puts ans
  end
}