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)

class BinaryIndexedTree
  def initialize(n, d)
    @n = n
    if d == 0 then
      @b = Array.new(@n, 0)
    else
      @b = (1..@n).map{|x| (x&-x)*d}
    end
  end
  def add(i, x)
    i += 1
    while i <= @n do
      @b[i-1] += x
      i += i&-i
    end
  end
  def sum(i)
    i+= 1
    ret = 0
    while i > 0 do
      ret += @b[i-1]
      i -= i&-i
    end
    ret
  end
end

N, Q = gets.chomp.split(" ").map(&:to_i)
C = gets.chomp.split(" ").map(&:to_i)
QU = Array.new(N){[]}
Q.times{|i|
  l, r = gets.chomp.split(" ").map(&:to_i)
  QU[r-1] << [l-1, i]
}

nxt = Array.new(N)
wk = Array.new(N)
bit = BinaryIndexedTree.new(N, 1)
ans = Array.new(N)
pnt = 0
QU.each_with_index{|w, r|
  while pnt <= r do
    bit.add(N-1-wk[C[pnt]], -1) if not wk[C[pnt]].nil?
    wk[C[pnt]] = pnt
    pnt += 1
  end
  w.each{|l, i|
    ans[i] = bit.sum(N-1-l) - (N-1-r)
  }
}

puts ans