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: Time Limit Exceeded)

class BIT
  def initialize(n)
    @size = n
    @data = Array.new(n + 1, 0)
  end
  def sum(l,r)
    s = 0
    while  l > 0 || r > 0
      s = s + @data[r] - @data[l]
      l = l - (l & -l)
      r = r - (r & -r)
    end
    return s
  end
  def add(i,x)
    while i <= @size
      @data[i] += x
      i += (i & -i)
    end
  end
end
A_ORD = 'a'.ord
N = gets.to_i
S = gets.chomp.chars
C = Array.new(26){ BIT.new(N + 1) }
(1 .. N).each do |i|
  C[S[i - 1].ord - A_ORD].add(i, 1)
end

Q = gets.to_i
Q.times do 
  q = gets.chomp.split
  t = q.shift.to_i
  if t == 1
    i = q.shift.to_i
    c = q.shift
    c_ = S[i - 1]
    if c_ != c
      C[c_.ord - A_ORD].add(i, -1)
      C[c.ord - A_ORD].add(i, 1)
      S[i - 1] = c
    end
  else
    l,r = q.map(&:to_i)
    puts C.count{|bit| bit.sum(l - 1, r) > 0 }
  end
end