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: Accepted)

GC.disable

class BinaryIndexTree
  attr_reader :bit, :size

  def initialize(size, init: 0)
    @bit = Array.new(size, init)
    @size = size
  end

  def sum(i)
    s = 0

    while i > 0
      s += bit[i]
      i -= i & -i
    end

    s
  end

  def add(i, x)
    while i < size
      bit[i] += x
      i += i & -i
    end
  end
end

N, Q = gets.split.map(&:to_i)
C = gets.split.map(&:to_i)
queries = Q.times.map.with_index { |i|
  l, r = gets.split.map(&:to_i)

  [i, l, r]
}

ans = Array.new(Q, -1)
last = Array.new(N + 1)
idx = 0
bit = BinaryIndexTree.new(N + 1)

queries.sort_by { |i, l, r| r }.each do |i, l, r|
  while idx < r
    c = C[idx]

    if last[c]
      bit.add(last[c], 1)
    end

    last[c] = idx + 1
    idx += 1
  end

  ans[i] = (r - l + 1) - (bit.sum(r) - bit.sum(l - 1))
end

puts ans