Problem:
Score : 600 points

Problem Statement

We have N colored balls arranged in a row from left to right; the color of the i-th ball from the left is c_i.

You are given Q queries. The i-th query is as follows: how many different colors do the l_i-th through r_i-th balls from the left have?

Constraints

1\leq N,Q \leq 5 \times 10^5

1\leq c_i \leq N

1\leq l_i \leq r_i \leq N

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N Q
c_1 c_2 \cdots c_N
l_1 r_1
l_2 r_2
:
l_Q r_Q

Output

Print Q lines. The i-th line should contain the response to the i-th query.

Sample Input 1

4 3
1 2 1 3
1 3
2 4
3 3

Sample Output 1

2
3
1

The 1-st, 2-nd, and 3-rd balls from the left have the colors 1, 2, and 1 - two different colors.

The 2-st, 3-rd, and 4-th balls from the left have the colors 2, 1, and 3 - three different colors.

The 3-rd ball from the left has the color 1 - just one color.

Sample Input 2

10 10
2 5 6 5 2 1 7 9 7 2
5 5
2 4
6 7
2 2
7 8
7 9
1 8
6 9
8 10
6 8

Sample Output 2

1
2
2
1
2
2
6
3
3
3

Solution in Ruby (2.7.1) (judge verdict: Wrong Answer)

require 'set'; require 'prime'; require 'pp'
INF=Float::INFINITY; MOD=10**9+7

class SegmentTree
  attr_accessor :a, :n
  def initialize(nums)
    return if nums.nil? || nums.empty?
    size = nums.size
    @n = 1
    while @n < size
      @n <<= 1
    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
  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
  # end

  def query(a, b, k=0, l=0, r=-1)
    r = @n-1 if r < 0
    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)
    lvalue.merge(rvalue)
  end

  def compare(x, y)
    x + y
  end

  def new_obj(obj=nil)
    Set.new([obj])
  end
end

n,q = gets.chomp.split.map(&:to_i)
c = gets.chomp.split.map(&:to_i)

seg = SegmentTree.new(c)
# p seg.a

q.times do
  l, r = gets.chomp.split.map(&:to_i)
  puts seg.query(l-1, r-1).size-1
end