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"
	"sort"
)

func main() {
	defer writer.Flush()
	N, Q := ReadInt(), ReadInt()
	c := append([]int{0}, ReadInts(N)...)
	lefts := make([]int, Q)
	rights := make([]int, Q)
	queryIDs := make([]int, Q)
	for q := 0; q < Q; q++ {
		queryIDs[q] = q
		lefts[q], rights[q] = ReadInt(), ReadInt()+1
	}
	sort.Slice(queryIDs, func(i, j int) bool {
		return rights[queryIDs[i]] < rights[queryIDs[j]]
	})

	t := MakeSegTree(N + 1)
	seen := make([]int, N+1)
	q := 0
	answers := make([]int, Q)
	for i := 1; i <= N; i++ {
		if seen[c[i]] > 0 {
			t.Add(seen[c[i]], -1)
		}
		t.Add(i, 1)
		seen[c[i]] = i
		for q < Q && i+1 == rights[queryIDs[q]] {
			answers[queryIDs[q]] = t.Sum(lefts[queryIDs[q]], rights[queryIDs[q]])
			q++
		}
	}
	for _, answer := range answers {
		Println(answer)
	}
}

type SegTree []int

func MakeSegTree(n_ int) SegTree {
	n := 1
	for n < n_ {
		n <<= 1
	}
	return make([]int, n*2)
}

func (t SegTree) Add(i, x int) {
	i += len(t) >> 1
	for i > 0 {
		t[i] += x
		i >>= 1
	}
}

func (t SegTree) Sum(a, b int) int {
	return t.sumRecur(a, b, 1, 0, len(t)>>1)
}
func (t SegTree) sumRecur(a, b, k, l, r int) int {
	if b <= l || r <= a {
		return 0
	}
	if a <= l && r <= b {
		return t[k]
	}
	v := 0
	v += t.sumRecur(a, b, k<<1, l, (l+r)>>1)
	v += t.sumRecur(a, b, k<<1+1, (l+r)>>1, r)
	return v
}

var reader = bufio.NewReader(os.Stdin)
var writer = bufio.NewWriter(os.Stdout)

func Scan(a ...interface{}) {
	if _, err := fmt.Fscan(reader, a...); err != nil {
		panic(err)
	}
}
func ReadInt() (i int) { Scan(&i); return }
func ReadInts(n int) []int {
	v := make([]int, n)
	for i := 0; i < n; i++ {
		Scan(&v[i])
	}
	return v
}
func Println(a ...interface{}) { fmt.Fprintln(writer, a...) }