BZOJ 3781: 小B的询问 [莫队]

求区间每种颜色出现次数平方和

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写裸题练手

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
using namespace std;
typedef long long ll;
const int N=5e4+5;
inline int read(){
    char c=getchar();int x=0,f=1;
    while(c<'0'||c>'9'){if(c=='-')f=-1;c=getchar();}
    while(c>='0'&&c<='9'){x=x*10+c-'0';c=getchar();}
    return x*f;
}

int n,a[N],Q,k, block,m,pos[N];
struct meow{
    int l,r,id;
    bool operator <(const meow &x) const {return pos[l]<pos[x.l] || (pos[l]==pos[x.l] && r<x.r);}
}q[N];

int c[N]; ll now=0,ans[N];
inline void add(int x) {now+=2*c[a[x]]+1; c[a[x]]++;}
inline void del(int x) {now-=2*c[a[x]]-1; c[a[x]]--;}
void solve(){
    int l=1,r=0;
    for(int i=1;i<=Q;i++){
        while(r<q[i].r) r++, add(r);
        while(r>q[i].r) del(r), r--;
        while(l<q[i].l) del(l), l++;
        while(l>q[i].l) l--, add(l);
        ans[q[i].id]=now;
    }
}
int main(){
    freopen("in","r",stdin);
    n=read();Q=read();k=read();
    block=sqrt(n); m=(n-1)/block+1;
    for(int i=1;i<=n;i++) a[i]=read(), pos[i]=(i-1)/block+1;
    for(int i=1;i<=Q;i++) q[i].l=read(), q[i].r=read(), q[i].id=i;
    sort(q+1, q+1+Q);
    solve();
    for(int i=1;i<=Q;i++) printf("%lld\n",ans[i]);
}