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 C++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

const int MAX_N = 5e5+10, MAX_Q = 5e5+10;
int N, Q;
int c[MAX_N];
int l[MAX_Q],r[MAX_Q];
vector<int> qry[MAX_N];
vector<int> qid[MAX_N];
int lst[MAX_N];
int dat[MAX_N];
int ans[MAX_Q];

void add(int i, int v)
{
	while(i<=N){
		dat[i]+=v;
		i+=i&-i;
	}
}

int sum(int i)
{
	int res = 0;
	while(i>0){
		res+=dat[i];
		i-=i&-i;
	}
	return res;
}

int rangesum(int i, int j)
{
	return sum(j)-sum(i-1);
}

void solve()
{
	for(int i=1;i<=N;++i){
		if(lst[c[i]]>0) add(lst[c[i]], -1);
		add(i,1);
		lst[c[i]]=i;
		for(int j=0;j<qry[i].size();++j){
			ans[qid[i][j]]=rangesum(qry[i][j],i);
		}
	}
	for(int i=0;i<Q;++i)cout<<ans[i]<<'\n';
}

int main()
{
	cin >> N >> Q;
	for(int i=1;i<=N;++i) cin >> c[i];
	for(int i=0;i<Q;++i){
		cin >> l[i] >> r[i];
		qry[r[i]].push_back(l[i]);
		qid[r[i]].push_back(i);
	}
	solve();
	return 0;
}