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)
A = 'a'.ord

class ST
  def initialize
    @a = S.chars.map{|c| c.ord - A}
    @n = 2**N.bit_length
    @t = Array.new(2*@n - 1, 0)
    (0 ... N).each{|i| @t[i + @n - 1] = 1<<@a[i]}
    (@n - 2).downto(0){|i| @t[i] = @t[2*i + 1] | @t[2*i + 2]}
  end

  def update(i, x)
    @t[i + @n - 1] -= 1<<@a[i]
    @a[i] = x
    @t[i + @n - 1] += 1<<x
    i += @n - 1
    while i > 0
      i = (i - 1)/2
      @t[i] = @t[2*i + 1] | @t[2*i + 2]
    end
  end

  def query(a, b, k = 0, l = 0, r = -1)
    r = @n if r < 0
    return 0 if b <= l || r <= a
    return @t[k] if a <= l && r <= b
    query(a, b, 2*k + 1, l, (l + r)/2) | query(a, b, 2*k + 2, (l + r)/2, r)
  end
end

s = ST.new
Qs.each do |a, b, c|
  if a == '1'
    s.update(b.to_i - 1, c.ord - A)
  else
    puts s.query(b.to_i - 1, c.to_i).to_s(2).count('1')
  end
end