【luogu P1972 [SDOI2009]HH的项链】 题解

题目链接：https://www.luogu.org/problemnew/show/P1972
真是不懂为什么要卡莫队！

#include <cmath>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 2000100;
int a[maxn], n, m, ans[maxn], last[maxn];
struct Query{
    int l, r, p;
}q[maxn];
bool cmp(const Query &a, const Query &b)
{
    return a.r<b.r;
}
struct BIT{
    int data[maxn], num;
    void add(int pos, int val)
    {
        while(pos <= num)
        {
            data[pos] += val;
            pos += (pos&(-pos));
        }
        return;
    }
    int sum(int pos)
    {
        int sum = 0;
        while(pos)
        {
            sum += data[pos];
            pos -= (pos&(-pos));
        }
        return sum;
    }
    int query(int l, int r)
    {
        return sum(r) - sum(l-1);
    }
}bit;
int main()
{
    scanf("%d",&n);
    for(int i = 1; i <= n; i++)
    scanf("%d",&a[i]);
    bit.num = n;
    scanf("%d",&m);
    for(int i = 1; i <= m; i++)
    {
        scanf("%d%d",&q[i].l,&q[i].r);
        q[i].p = i;
    }
    sort(q+1,q+1+m,cmp);
    int Q = 0;
    for(int i = 1; i <= m; i++)
    {
        while(Q < q[i].r)
        {
            Q+=1;
            if(last[a[Q]])
            {
                bit.add(last[a[Q]],-1);
                bit.add(Q,1);
                last[a[Q]] = Q;
            }
            else
            {
                bit.add(Q,1);
                last[a[Q]] = Q;
            }
        }
        ans[q[i].p] = bit.query(q[i].l,q[i].r);
    }
    for(int i = 1; i <= m; i++)
    printf("%d\n",ans[i]);
    return 0;
}