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)

N = gets.to_i
S = gets.chomp.chars
Q = gets.to_i.times.map{ gets.split }

L = 1 << N.bit_length
A_ORD = 'a'.ord

ST = Array.new(26){ Array.new(2 * L, 0) }
S.each_with_index do |c,j|
  ST[c.ord - A_ORD][L + j] = 1
end

class << ST
  # range query with [a,b) 
  def kind(a, b)
    26.times.count{|i| kind_dfs(i, a, b, 1, 0, L) > 0 }
  end
  
  def kind_dfs(i, a, b, k, l, r)
    return 0 if b <= l || r <= a
    return self[i][k] if a <= l && r <= b
    mid = (l + r) / 2
    return kind_dfs(i, a, b, 2 * k, l, mid) + kind_dfs(i, a, b, 2 * k + 1, mid, r)
  end
  
  def swap(i, from, to)
    j = L + i
    while j > 0
      self[from][j] -= 1
      self[to][j] += 1
      j /= 2
    end
  end
  def build_dfs(i,j)
    if j < L
      self[i][j] = build_dfs(i, 2 * j) + build_dfs(i, 2 * j + 1)
    else
      self[i][j]
    end
  end
  def build
    26.times do |i|
      build_dfs(i, 1)
    end
  end
end

ST.build
Q.each do |q|
  t = q.shift.to_i
  if t == 1
    i = q.shift.to_i - 1
    to = q.shift
    from = S[i]
    if from != to
      ST.swap(i, from.ord - A_ORD, to.ord - A_ORD)
      S[i] = to
    end
  else
    a,b = q.map(&:to_i)
    puts ST.kind(a - 1, b)
  end
end