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;
const int maxn = 5e5 + 10;
int n, q, m;
int ans[maxn], cnt[maxn], c[maxn];
struct Query
{
	int l, r, id, L;
}a[maxn];
bool cmp(const Query & i, const Query & j) { return i.L < j.L || (i.L == j.L && i.r < j.r);}
int main()
{
	scanf("%d%d", &n, &q);
	m = sqrt(q);
	for(int i = 1; i <= n; ++i) scanf("%d", &c[i]);
	for(int i = 1; i <= q; ++i) 
	{
		scanf("%d%d", &a[i].l, &a[i].r);
		a[i].L = a[i].l / m;
		a[i].id = i;
	}
	sort(a + 1, a + q + 1, cmp);
	int l = 0, r = 0, res = 0;
	for(int i = 1; i <= q; ++i)
	{
		while(r < a[i].r)
		{
			++r;
			if(!cnt[c[r]]) ++res;
			++cnt[c[r]];
		}
		while(r > a[i].r)
		{
			--cnt[c[r]];
			if(!cnt[c[r]]) --res;
			--r;
		}
		while(l < a[i].l)
		{
			--cnt[c[l]];
			if(!cnt[c[l]]) --res;
			++l;
		}
		while(l > a[i].l)
		{
			--l;
			if(!cnt[c[l]]) ++res;
			++cnt[c[l]];
		}	
		ans[a[i].id] = res;
	}
	for(int i = 1; i <= q; ++i) printf("%d\n", ans[i]);
	return 0;
}