SPOJ - DQUERY D-query （莫队）

题目链接：https://vjudge.net/problem/SPOJ-DQUERY

解题思路：

莫队

代码：

#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<map>
#define ll long long
#define for0(i,a,b) for (int i = a; i < b; i++)
#define for1(i,a,b) for (int i = a; i <= b; i++)

using namespace std;

const int N = 3e4+5;
const int M = 2e5+5;
const int MAXV = 1e6+5;

int blo,bl[N],m,n;
int v[N];
int sum;
int cnt[MAXV];
int ans[M];

struct node
{
    int l,r;
    int id;
    bool operator < (const node& a)const{
        if (bl[l]==bl[a.l]) return r < a.r;
        return bl[l] < bl[a.l];
    }
}q[M];

void REMOVE(int x)
{
    cnt[v[x]]--;
    if (cnt[v[x]]==0) sum--;
}

void ADD(int x)
{
    cnt[v[x]]++;
    if (cnt[v[x]]==1) sum++;
}

void solve()
{
    int nowl = 1,nowr = 0;
    for1(i,1,m){
        int tl = q[i].l,tr = q[i].r;
        while (nowr<tr) ADD(++nowr);
        while (nowl>tl) ADD(--nowl);
        while (nowr>tr) REMOVE(nowr--);
        while (nowl<tl) REMOVE(nowl++);
        ans[q[i].id] = sum;
    }
}

int main()
{
    scanf("%d",&n);
    blo = sqrt(n);
    for1(i,1,n){
        scanf("%d",v+i);
        bl[i] = (i-1)/blo+1;
    }

    scanf("%d",&m);
    for1(i,1,m){
        scanf("%d %d",&q[i].l,&q[i].r);
        q[i].id = i;
    }
    sort(q+1,q+1+m);

    solve();
    for1(i,1,m){
        printf("%d\n",ans[i]);
    }
    return 0;
}