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: Time Limit Exceeded)

#include<bits/stdc++.h>
using namespace std;
int n,q,xl,xr,res;
int a[500010],cnt[500010],ans[500010];
struct Node{
	int l,r,num;
}f[500010];
inline bool cmp(Node a,Node b){
	if(a.l/800==b.l/800)
		return a.r<b.r;
	return a.l<b.l;
}
inline void Add(int x){
	if(cnt[x]==0)
		res++;
	cnt[x]++;
}
inline void Delete(int x){
	if(cnt[x]==1)
		res--;
	cnt[x]--;
}
int main(){
	cin>>n>>q;
	for(int i=1;i<=n;i++)
		cin>>a[i];
	for(int i=1;i<=q;i++){
		cin>>f[i].l>>f[i].r;
		f[i].num=i;
	}
	sort(f+1,f+q+1,cmp);
	xl=1,xr=1,res=1;
	cnt[a[1]]=1;
	for(int i=1;i<=q;i++){
		while(xl<f[i].l){
			Delete(a[xl]);
			xl++;
		}
		while(xl>f[i].l){
			xl--;
			Add(a[xl]);
		}
		while(xr<f[i].r){
			xr++;
			Add(a[xr]);
		}
		while(xr>f[i].r){
			Delete(a[xr]);
			xr--;
		}
		ans[f[i].num]=res;
	}
	for(int i=1;i<=q;i++)
		cout<<ans[i]<<endl;
	return 0;
}