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>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

int main(){
    int n;
    scanf("%d",&n);
    int q;
    scanf("%d",&q);
    vector<int> c(n);
    rep(i,n) scanf("%d",&c[i]),--c[i];
    vector<int> l(q),r(q);
    rep(i,q){
        scanf("%d %d",&l[i],&r[i]);
        --l[i];
    }

    int sq = sqrt(n);
    vector<int> qi(q,0);
    for(int i=0;i<q;i++) qi[i] = i;
    sort(qi.begin(),qi.end(),[&](const int &i,const int &j){
        if(l[i] / sq != l[j] / sq) return l[i] < l[j];
        return r[i] < r[j];
    });

    vector<int> cnt(n,0);
    int ans = 0;

    auto add = [&](int id){
        //if(id<0 ||id>=n) return;
        if(cnt[c[id]]==0) ++ans;
        ++cnt[c[id]];
    };

    auto del = [&](int id){
        //if(id<0 ||id>=n) return;
        if(cnt[c[id]]==1) --ans;
        --cnt[c[id]];
    };

    
    vector<int> queryans(q);
    int nl = 0,nr = 0;
    for(int i:qi){
        //cout << nl << " " << nr  << endl;
        while(nl > l[i]) --nl,add(nl);
        while(nr < r[i]) add(nr),++nr;
        while(nl < l[i]) del(nl),++nl;
        while(nr > r[i]) --nr,del(nr);

        queryans[i] = ans;
    }

    rep(i,q) printf("%d\n",queryans[i]);
    return 0;
}