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 SegmentTree
  # 配列（もしくは配列のサイズ）、初期値、function
  def initialize(n, unity, &func)
    raise ArgumentError if !n || !block_given?
    @size_r = 1
    @n = (n.is_a?(Array) ? n.size : n)
    while @size_r < @n
      @size_r <<= 1
    end
    @func = func
    # 初期値
    @unity = unity
    @data = Array.new(@size_r * 2, @unity)
    # 配列が渡された場合、初期値をセットして辺を張る
    if n.is_a?(Array)
      @n.times { |i| @data[i + @size_r] = n[i] }
      self.build()
    end
  end

  # 0-indexed
  def set(index, value)
    raise IndexError if index >= @n
    @data[index + @size_r] = value
  end

  # 辺を張る
  def build
    (@size_r - 1).downto(1) do |k|
      @data[k] = @func.call(@data[k * 2], @data[k * 2 + 1])
    end
  end

  # 0-indexed
  def update(index, value)
    raise IndexError if index >= @n
    index += @size_r
    @data[index] = value
    index >>= 1
    while index > 0
      @data[index] = @func.call(@data[index * 2], @data[index * 2 + 1])
      index >>= 1
    end
    true
  end

  # 0-indexed b を含まず
  def get(a, b)
    raise IndexError if a > @n || b > @n || a > b
    vleft = vright = @unity
    left = a + @size_r
    right = b + @size_r
    while (left < right)
      if left.odd?
        vleft = @func.call(vleft, @data[left])
        left += 1
      end
      if right.odd?
        right -= 1
        vright = @func.call(@data[right], vright)
      end
      left >>= 1
      right >>= 1
      return true if vleft || vright
    end
    @func.call(vleft, vright)
  end

  def [](k)
    @data[@size_r + k]
  end
end

n = gets.to_i
s = gets.chomp.split("")
q = gets.to_i
queries = []
q.times do
  tmp = gets.chomp.split
  tmp[0] = tmp[0].to_i
  tmp[1] = tmp[1].to_i
  tmp[2] = tmp[2].to_i if tmp[0] == 2
  queries << tmp
end
segs = 26.times.map { SegmentTree.new(n, false) { |x, y| x || y } }
s.each_with_index do |c, i|
  segs[c.ord - 97].update(i, true)
end
ans = []
queries.each do |a, b, c|
  if a == 1
    prev = s[b - 1]
    s[b - 1] = c
    segs[prev.ord - 97].update(b - 1, false)
    segs[c.ord - 97].update(b - 1, true)
  else
    sum = 0
    26.times do |i|
      sum += 1 if segs[i].get(b - 1, c)
    end
    ans << sum
  end
end
ans.each { |a| puts a }