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.to_i

class SegmentTree
  def initialize(arr)
    @size = 1 << (arr.length-1).bit_length
    @tree = Array.new(@size*2+1,0)
    init(arr)
  end
  
  def init(arr)
    arr.each.with_index do |v, i|
      set(v,@size+i-1)
    end
    (@size - 2).downto(0) do |i|
      merge(i)
    end
  end

  # ここを実装する
  def set(v,i)
    @tree[i] = 1 << (v.ord - 'a'.ord)
  end

  # ここも実装する
  def merge_f(a,b)
    a | b
  end
  
  def merge(i)
    @tree[i] = merge_f(@tree[i * 2 + 1], @tree[i * 2 + 2])
  end
  
  def update(v,i)
    i = @size + i - 1
    set(v,i)
    while 0 < i
      i = (i - 1) / 2
      merge(i)
    end
  end
  
  def query(a,b)
    query_(a,b,0,0,@size)
  end
  
  def query_(a,b,k,l,r)
    return 0 if r <= a || b <= l
    return @tree[k] if a <= l && r <= b
    mid = (l+r)/2
    vl = query_(a, b, k * 2 + 1, l, mid)
    vr = query_(a, b, k * 2 + 2, mid, r)
    merge_f(vl,vr)
  end
end

st = SegmentTree.new(s.chars)

$<.read.split.each_slice(3).each do |a, b, c|
  if a == '1'
    st.update(c,b.to_i-1)
  else
    p st.query(b.to_i - 1, c.to_i).to_s(2).count('1')
  end
end