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)

class SegmentTree
  def initialize(nums)
    return if nums.nil? || nums.empty?
    size = nums.size
    @n = 1
    while @n < size
      @n *= 2
    end
    @a = Array.new(@n*2-1){new_obj}

    size.times do |i|
      @a[@n + i - 1] = new_obj(nums[i])
    end
    (@n-2).downto(0) do |i|
      @a[i] = compare(@a[i*2+1], @a[i*2+2])
    end
    # p ['initialize', @a]
  end

  def update(i, val)
    i += @n - 1
    @a[i] = new_obj(val)
    while i > 0
      i = (i-1)/2
      @a[i] = compare(@a[i*2+1], @a[i*2+2])
    end
    # p ['update', @a]
  end

  def query(a, b, k=0, l=0, r=-1)
    r = @n-1 if r < 0
    # p [[a,b],k,[l,r], b <= l || r <= a, a <= l && r <= b]
    return new_obj if b < l || r < a # not cover
    return @a[k]   if a <= l && r <= b # cover all

    lvalue = query(a, b, 2*k+1, l, (l+r)/2)
    rvalue = query(a, b, 2*k+2, (l+r)/2+1, r)
    return compare(lvalue, rvalue)
  end

  def compare(x, y)
    x | y
  end

  def new_obj(obj=0)
    obj
  end
end

require 'set'; require 'prime'
INF=Float::INFINITY; MOD=10**9+7
n = gets.chomp.to_i
s = gets.chomp
q = gets.chomp.to_i

init_a = Array.new(n)
n.times do |i|
  cnum = s[i].ord - 97
  init_a[i] = 1 << cnum
end

st = SegmentTree.new(init_a)
q.times do
  type, i, c = gets.chomp.split

  if type == '1'
    st.update(i.to_i - 1, 1 << (c.ord - 97))
  else
    r = st.query(i.to_i - 1, c.to_i - 1)
    puts r.to_s(2).split(//).map{|num| num.to_i}.inject(&:+)
  end
end