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D-QUERY

                                             D-Query

                                           segment tree + offline method

#include <iostream>
#include <algorithm>
#include <stdio.h>
#include <map>
#define sf(i) scanf("%d", &i)
#define pf(i) printf("%d\n", i)

using namespace std;

const int N = 30001;
const int Q = 200001;

struct node
{
    int l, r;
    int pos,
    int val;
};

int n, q;
node arr[N + Q];
int result[Q];
int seg[4 * N];
map<int, int> last_pos;

node makenode(int l, int r, int pos, int val)
{
    node temp;
    temp.l = l;
    temp.r = r;
    temp.pos = pos;
    temp.val = val;

    return temp;
}

void update(int l, int r, int index, int pos, int val)
{
    if(l == r)
    {
        seg[index] = val;
    }
    else
    {
        int mid = (r + l) / 2;
        if(pos <= mid)
        {
            update(l, mid, 2 * index, pos, val);
        }
        else
        {
            update(mid + 1, r, 2 * index + 1, pos, val);
        }
        seg[index] = seg[index << 1] + seg[(index << 1) + 1];
    }
}

int query(int l, int r, int index, int qs, int qe)
{
    if(qs > r || qe < l)
        return 0;
    if(qs <= l && qe >= r)
        return seg[index];

    int mid = (l + r) / 2;
    int a = query(l, mid, 2 * index, qs, qe);
    int b = query(mid + 1, r, 2 * index + 1, qs, qe);
    return a + b;
}

bool comp(node a, node b)
{
    if(a.pos == b.pos)
    {
        return a.r < b.r;
    }
    return (a.pos < b.pos);
}

int main()
{
    int l, r;
    sf(n);
    int index = 0;
    int temp;
    for(int i = 1; i <= n; i++)
    {
        sf(temp);
        arr[index++] = makenode(-1, -1, i, temp);
    }

    sf(q);
    for(int i = 1; i <= q; i++)
    {
        sf(l), sf(r);
        arr[index++] = makenode(l, r, r, i); // stores position as value in case of query
    }

    sort(arr, arr + index, comp);

    for(int i = 0; i < index; i++)
    {
        if(arr[i].l == -1 && arr[i].r == -1)
        {
            if(last_pos[arr[i].val] == 0)
            {
                update(1, n, 1, arr[i].pos, 1); //if value does not exist update the pos with 1
            }
            else
            {
                update(1, n, 1, last_pos[arr[i].val], 0); // if value already exist then update the old pos with 0
                update(1, n, 1, arr[i].pos, 1); // update the new pos with 1
            }
            last_pos[arr[i].val] = arr[i].pos; // update the last position array
        }
        else
        {
            int ans = query(1, n, 1, arr[i].l, arr[i].r);
            result[arr[i].val] = ans;
        }
    }

    for(int i = 1; i <= q; i++)
    {
        pf(result[i]);
    }

    return 0;
}

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