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"
	"bytes"
	"fmt"
	"io"
	"os"
	"sort"
	"strconv"
)

var DEBUG = false

type Query struct {
	l, r int
	id   int
	ans  int
}

func main() {
	defer Flush()
	N := readi()
	Q := readi()
	_, c := readInts(N)
	for i := range c {
		c[i]--
	}

	q := make([]Query, Q)
	for i := range q {
		q[i].l = readi() - 1
		q[i].r = readi() - 1
		q[i].id = i
	}
	sort.Slice(q, func(i, j int) bool {
		return q[i].r < q[j].r
	})

	last := make([]int, N)
	for i := range last {
		last[i] = -1
	}
	for i, v := range c {
		if q[0].r < i {
			break
		}
		last[v] = i
	}

	a := make([]int, N)
	for i := range last {
		if last[i] == -1 {
			continue
		}
		a[last[i]] = 1
	}

	b := NewBIT(a)

	rx := q[0].r
	for i := range q {
		if rx < q[i].r {
			dbg("new rx", rx, "->", q[i].r)
			bitdbg(b)
			for j := rx + 1; j <= q[i].r; j++ {
				v := c[j]
				if last[v] != -1 {
					b.Add(last[v], -1)
				}
				last[v] = j
				b.Add(j, 1)
			}
			bitdbg(b)
			rx = q[i].r
		}
		dbg("query", q[i].l, q[i].r+1)
		q[i].ans = b.Sum(q[i].l, q[i].r+1)
	}

	sort.Slice(q, func(i, j int) bool {
		return q[i].id < q[j].id
	})
	for i := range q {
		println(q[i].ans)
	}

}

func bitdbg(b *BIT) {
	if !DEBUG {
		return
	}
	for i := 0; i < len(b.a)-1; i++ {
		dbgf(" %d", b.Sum(i, i+1))
	}
	dbg()
}

// BIT represents the Binary Indexed Tree
type BIT struct {
	a []int
}

// NewBIT returns the pointer to a BIT for the slice.
func NewBIT(a []int) *BIT {
	b := &BIT{
		a: make([]int, len(a)+1),
	}

	copy(b.a[1:], a)
	for d, ok := 2, true; ok; d *= 2 {
		ok = false
		for i := d; i < len(b.a); i += d {
			b.a[i] += b.a[i-d/2]
			ok = true
		}
	}
	return b
}

// Sum0N returns the sum of [0, n)
func (b *BIT) Sum0N(n int) int {
	var res int
	for i := n; 0 < i; i = i - i&(-i) {
		res += b.a[i]
	}
	return res
}

// Sum0N returns the sum of the range [i, j)
func (b *BIT) Sum(i, j int) int {
	return b.Sum0N(j) - b.Sum0N(i)
}

// Add updates the value at index i adding the diff.
func (b *BIT) Add(i int, diff int) {
	for j := i + 1; j < len(b.a); j = j + j&(-j) {
		b.a[j] += diff
	}
}

// Update updates the value at index i.
func (b *BIT) Update(i int, v int) {
	prev := b.Sum(i, i+1)
	diff := v - prev
	b.Add(i, diff)
}

// -----------------------------------------------------------------------------

// IO helper functions

// Returns next token from input.  It must be initialized by SetInput()
// before the first call.
var nextToken func() ([]byte, error)
var nextLine func() ([]byte, error)

// Holds a buffer for output.  It must be initialized by SetOutput().
// All IO fucntions (read*() and [e]print*()) should write to OutputWriter
// instead of this.
var OutputBuffer *bufio.Writer

// Holds an io.Writer.  It must be initialized by SetOutput()
var OutputWriter io.Writer

// Set IO functions for interactive input/output.
func SetInteractive(w io.Writer, r io.Reader) {
	SetUnbefferedInput(r)
	OutputBuffer = nil
	OutputWriter = w
}

// Setup OutputBuffer and OutputWriter.
func SetOutput(w io.Writer) {
	OutputBuffer = bufio.NewWriter(w)
	OutputWriter = OutputBuffer
}

// Flushes OutputBuffer
func Flush() {
	if OutputBuffer != nil {
		OutputBuffer.Flush()
	}
}

// Returns true if c is a white space
func IsSpace(c byte) bool {
	switch c {
	case '\t', '\n', '\v', '\f', '\r', ' ':
		return true
	}
	return false
}

func IsNewLine(c byte) bool {
	switch c {
	case '\n', '\r':
		return true
	}
	return false
}

// Setup nextToken with input buffer.
func SetInput(r io.Reader) {
	buf := new(bytes.Buffer)
	var b []byte

	var i int
	rest := func() ([]byte, error) {
		for i < len(b) && IsSpace(b[i]) {
			i++
		}
		if i == len(b) {
			return nil, io.ErrUnexpectedEOF
		}
		j := i
		for i < len(b) && !IsSpace(b[i]) {
			i++
		}
		return b[j:i], nil
	}
	initial := func() ([]byte, error) {
		io.Copy(buf, r)
		b = buf.Bytes()
		nextToken = rest
		return rest()
	}
	nextToken = initial

	restLn := func() ([]byte, error) {
		for i < len(b) && IsNewLine(b[i]) {
			i++
		}
		if i == len(b) {
			return nil, io.ErrUnexpectedEOF
		}
		j := i
		for i < len(b) && !IsNewLine(b[i]) {
			i++
		}
		return b[j:i], nil
	}

	initialLn := func() ([]byte, error) {
		io.Copy(buf, r)
		b = buf.Bytes()
		nextLine = restLn
		return restLn()
	}
	nextLine = initialLn
}

// Setup nextToken without input buffer.
func SetUnbefferedInput(r io.Reader) {
	buf := bufio.NewReader(r)
	var b []byte

	var i int
	nextToken = func() ([]byte, error) {
		var err error
		if i == len(b) {
			b, err = buf.ReadBytes('\n')
			if err != nil {
				return nil, err
			}
			i = 0
			j := len(b) - 1
			for 0 <= j && IsSpace(b[j]) {
				j--
			}
			b = b[0 : j+1]
		}
		for i < len(b) && IsSpace(b[i]) {
			i++
		}
		j := i
		for i < len(b) && !IsSpace(b[i]) {
			i++
		}
		if i == j {
			return nil, io.ErrUnexpectedEOF
		}
		return b[j:i], nil
	}
}

// -----------------------------------------------------------------------------

// IO functions

// Reads next token and return it as []byte
func readb() []byte {
	b, err := nextToken()
	if err != nil {
		panic(err)
	}
	return b[:len(b):len(b)]
}

func readberr() ([]byte, error) {
	b, err := nextToken()
	return b[:len(b):len(b)], err
}

// Reads next token and return it as string
func reads() string {
	return string(readb())
}

func readserr() (string, error) {
	b, err := readberr()
	return string(b), err
}

// Read next line as []byte.  Trailing '\n' will not be included.
// See also comments on readb()
func readbln() []byte {
	b, err := nextLine()
	if err != nil {
		panic(err)
	}
	return b[:len(b):len(b)]
}

func readblnerr() ([]byte, error) {
	b, err := nextLine()
	return b[:len(b):len(b)], err
}

// Read next line as string
func readsln() string {
	return string(readbln())
}

func readslnerr() (string, error) {
	b, err := readblnerr()
	return string(b), err
}

// Reads next token and return it as int64
func readll() int64 {
	i, err := strconv.ParseInt(reads(), 10, 64)
	if err != nil {
		panic(err.Error())
	}
	return i
}

func readllerr() (int64, error) {
	s, err := readserr()
	if err != nil {
		return 0, fmt.Errorf("reading string: %w", err)
	}

	i, err := strconv.ParseInt(s, 10, 64)
	if err != nil {
		return 0, fmt.Errorf("parsing int: %w", err)
	}

	return i, nil
}

// Reads next token and return it as int
func readi() int {
	return int(readll())
}

func readierr() (int, error) {
	i, err := readllerr()
	return int(i), err
}

// Reads next token and return it as float64
func readf() float64 {
	f, err := strconv.ParseFloat(reads(), 64)
	if err != nil {
		panic(err.Error())
	}
	return f
}

func readferr() (float64, error) {
	s, err := readserr()
	if err != nil {
		return 0, fmt.Errorf("reading string: %w", err)
	}

	f, err := strconv.ParseFloat(s, 64)
	if err != nil {
		return 0, fmt.Errorf("parsing float: %w", err)
	}

	return f, nil
}

// Write args to OutputWriter with the format f
func printf(f string, args ...interface{}) (int, error) {
	return fmt.Fprintf(OutputWriter, f, args...)
}

// Write args to OutputWriter without format
func println(args ...interface{}) (int, error) {
	return fmt.Fprintln(OutputWriter, args...)
}

// Write args to stderr with the format f
func eprintf(f string, args ...interface{}) (int, error) {
	return fmt.Fprintf(os.Stderr, f, args...)
}

// Write args to stderr without format
func eprintln(args ...interface{}) (int, error) {
	return fmt.Fprintln(os.Stderr, args...)
}

func dbgf(f string, args ...interface{}) {
	if !DEBUG {
		return
	}
	fmt.Fprintf(os.Stderr, f, args...)
}

func dbg(args ...interface{}) {
	if !DEBUG {
		return
	}
	fmt.Fprintln(os.Stderr, args...)
}

// -----------------------------------------------------------------------------

// Utilities

func sumSlice(a []int) int {
	var res int
	for _, v := range a {
		res += v
	}
	return res
}

func sumSlicell(a []int64) int64 {
	var res int64
	for _, v := range a {
		res += v
	}
	return res
}

func readInts(N int) (int, []int) {
	if N == 0 {
		N = readi()
	}
	a := make([]int, N)
	for i := range a {
		a[i] = readi()
	}
	return N, a
}

func readIntsll(N int) (int, []int64) {
	if N == 0 {
		N = readi()
	}
	a := make([]int64, N)
	for i := range a {
		a[i] = readll()
	}
	return N, a
}

// -----------------------------------------------------------------------------

// Simple math functions

const (
	// big prime
	INF  = 1000000007
	INF2 = 1000000009
	INF3 = 998244353
)

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func minll(a, b int64) int64 {
	if a < b {
		return a
	}
	return b
}

func minf(a, b float64) float64 {
	if a < b {
		return a
	}
	return b
}

func max(a, b int) int {
	if a < b {
		return b
	}
	return a
}

func maxll(a, b int64) int64 {
	if a < b {
		return b
	}
	return a
}

func maxf(a, b float64) float64 {
	if a < b {
		return b
	}
	return a
}

func abs(a int) int {
	if a < 0 {
		return -a
	}
	return a
}

func absll(a int64) int64 {
	if a < 0 {
		return -a
	}
	return a
}

func absf(a float64) float64 {
	if a < 0 {
		return -a
	}
	return a
}

// egcd(a, b) returns d, x, y:
//   d is gcd(a,b)
//   x, y are  integers that satisfy ax + by = d
func egcd(a, b int) (int, int, int) {
	if b == 0 {
		return a, 1, 0
	}
	d, x, y := egcd(b, a%b)
	return d, y, x - a/b*y
}

func egcdll(a, b int64) (int64, int64, int64) {
	if b == 0 {
		return a, 1, 0
	}
	d, x, y := egcdll(b, a%b)
	return d, y, x - a/b*y
}

func gcd(a, b int) int {
	d, _, _ := egcd(a, b)
	return d
}

func gcdll(a, b int64) int64 {
	d, _, _ := egcdll(a, b)
	return d
}

// set up IO functions
func init() {
	// for non-interactive
	SetInput(os.Stdin)
	SetOutput(os.Stdout)

	// Enable below when interactive.  Its ok to leave above intact.
	// SetInteractive(os.Stdout, os.Stdin)
}