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 Go (1.14.1) (judge verdict: Accepted)

package main

import (
	"bufio"
	"fmt"
	"os"
)

// BIT (A Binary indexed tree or Fenwick tree)
type BIT struct {
	n int
	d []int
}

func NewBIT(n int, a ...int) *BIT {
	b := BIT{}
	b.n = n
	b.d = make([]int, n+1)
	for i := 0; i < len(a); i++ {
		b.Add(i, a[i])
	}
	return &b
}

func (b BIT) Add(i, x int) {
	for i++; i <= b.n; i += i & -i {
		b.d[i] += x
	}
}

func (b BIT) Sum(i int) int {
	x := 0
	for i++; i > 0; i -= i & -i {
		x += b.d[i]
	}
	return x
}

type query struct {
	l, r, i int
}

func main() {
	r := bufio.NewReader(os.Stdin)
	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()

	var n, q int
	fmt.Fscan(r, &n, &q)
	c := make([]int, n+1)
	qm := make(map[int][]query)

	for i := 1; i <= n; i++ {
		fmt.Fscan(r, &c[i])
	}
	for i := 0; i < q; i++ {
		var x, y int
		fmt.Fscan(r, &x, &y)
		qm[y] = append(qm[y], query{x, y, i})
	}

	ans := make([]int, q)
	ci := make([]int, n+1)
	b := NewBIT(n + 1)
	for i := 1; i <= n; i++ {
		if ci[c[i]] > 0 {
			b.Add(ci[c[i]], -1)
		}
		ci[c[i]] = i
		b.Add(i, 1)
		for _, v := range qm[i] {
			ans[v.i] = b.Sum(v.r) - b.Sum(v.l-1)
		}
	}
	for i := 0; i < q; i++ {
		fmt.Fprintln(w, ans[i])
	}
}