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: Runtime Error)

#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int, int>;
using G = vector<vector<int>>;
    
struct Mo {
    vector<int> left, right, index; // the interval's left, right, index
    vector<bool> v;
    int window;
    int nl, nr, ptr;
    
    Mo(int n) : window((int)sqrt(n)), nl(0), nr(0), ptr(0), v(n, false) { }
    
    /* push */
    void push(int l, int r) { left.push_back(l), right.push_back(r); }
    
    /* sort intervals */
    void build() {
        index.resize(left.size());
        iota(index.begin(), index.end(), 0);
        sort(begin(index), end(index), [&](int a, int b)
        {
            if (left[a] / window != left[b] / window) return left[a] < left[b];
            return bool((right[a] < right[b]) ^ (left[a] / window % 2));
        });
        
        //        sort(index.begin(), index.end(), [&](int a, int b) {
        //            if (left[a] / window != right[b] / window) return left[a] < left[b];
        //            else return right[a] < right[b];
        //        });
    }
    
    /* extend-shorten */
    void extend_shorten(int id) {
        v[id].flip();
        if (v[id]) insert(id);
        else erase(id);
    }
    
    /* next id of interval */
    int next() {
        if (ptr == index.size()) return -1;
        int id = index[ptr];
        while (nl > left[id]) extend_shorten(--nl);
        while (nr < right[id]) extend_shorten(nr++);
        while (nl < left[id]) extend_shorten(nl++);
        while (nr > right[id]) extend_shorten(--nr);
        return index[ptr++];
    }
    
    /* insert, erase (to be set appropriately) */
    void insert(int id);
    void erase(int id);
};

int N, Q;
int A[300001];
int res[200001];
int cnt[1000001];
int num_kind = 0;

void Mo::insert(int id) {
    int val = A[id];
    if (cnt[val] == 0) ++num_kind;
    ++cnt[val];
}

void Mo::erase(int id) {
    int val = A[id];
    --cnt[val];
    if (cnt[val] == 0) --num_kind;
}

int main() {
    scanf("%d", &N);
    scanf("%d", &Q);
    for(int i = 0; i < N; i++) scanf("%d", &A[i]);
    Mo mo(N);
    for(int i = 0; i < Q; i++) {
        int l, r; scanf("%d %d", &l, &r);
        mo.push(--l, r);
    }
    mo.build();
    for(int i = 0; i < Q; i++) res[mo.next()] = num_kind;
    for(int i = 0; i < Q; i++) printf("%d\n", res[i]);
}