TheAlgorithms-C-Plus-Plus/Range queries/MO.cpp

#include "bits/stdc++.h"
using namespace std;
const int N = 1e6+5;
int a[N],bucket[N],cnt[N];
int bucket_size;
struct query{
	int l,r,i;
}q[N];
int ans=0;

void add(int index)
{
	cnt[a[index]]++;
	if(cnt[a[index]] == 1)
		ans++;
}
void remove(int index)
{
	cnt[a[index]]--;
	if(cnt[a[index]] == 0)
		ans--;
}


bool mycmp(query x, query y)
{
	if(x.l/bucket_size != y.l/bucket_size)
		return x.l/bucket_size < y.l/bucket_size;
	return x.r<y.r;
}

int main() {
	int n,t,i,j,k=0;
	scanf("%d",&n);
	for(i=0;i<n;i++)
		scanf("%d",&a[i]);					
	bucket_size = ceil(sqrt(n));
	scanf("%d",&t);
	for(i=0;i<t;i++)
	{
		scanf("%d %d",&q[i].l,&q[i].r);
		q[i].l--;	q[i].r--;
		q[i].i = i;
	}
	sort(q,q+t,mycmp);
	int left=0,right=0;
	for(i=0;i<t;i++)
	{
		int L=q[i].l, R=q[i].r;
		while(left < L)
		{
			remove(left);
			left++;
		}
		while(left>L)
		{
			add(left-1);
			left--;
		}
		while(right<=R)
		{
			add(right);
			right++;
		}
		while(right>R+1)
		{
			remove(right-1);
			right--;
		}
		bucket[q[i].i] = ans; 
	}
	for(i=0;i<t;i++)
		printf("%d\n",bucket[i]);
	return 0;
}