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 "numo/narray"

class BIT
  def initialize(size)
    @n, @a = size, Numo::Int64.zeros(size + 1)
  end

  def query(i)
    s = 0
    while i > 0
      s = s + @a[i]
      i -= i & -i
    end
    s
  end

  def update(i, x)
    while i <= @n
      @a[i] = @a[i] + x
      i += i & -i
    end
  end
end

n, q = gets.split.map &:to_i
prevs = [-1] * n
ranges = []

gets.split.each_with_index do |c, i|
  c = c.to_i - 1
  if prevs[c] >= 0
    ranges << [q, prevs[c], i]
  end
  prevs[c] = i
end

q.times do |i|
  l, r = gets.split.map &:to_i
  ranges << [i, l-1, r-1]
end

ranges = ranges.sort_by { |(i, x, y)| -x * q - i }
tree = BIT.new(n)

results = []

ranges.each do |(i, x, y)|
  if i == q
    tree.update(y, 1)
  else
    results[i] = y - x + 1 - tree.query(y)
  end
end

puts results