小Z的袜子

莫队模板题，初学莫队感觉分块真是神奇。

#include <bits/stdc++.h>
using namespace std;
#define fst first
#define scd second
#define pb(x) push_back((x))
#define mkp(x,y) make_pair((x),(y)) 
#define ist(x) insert((x))
typedef long long ll;
typedef pair<int ,int > pii;
typedef pair<ll ,ll > pll;
typedef vector< int > vi;
ll gcd(ll a,ll b){ return b==0?a:gcd(b,a%b);}
ll qPow(ll a,ll b,ll mod){ ll ret=1ll;while(b){ if(b&1) ret=ret*a%mod;a=a*a%mod;b>>=1;} return ret; }

int N,M;
int chunk;
int a[50000+5];
int id[50000+5];
pii query[50000+5];
pll ans[50000+5];
int num[50000+5];

bool cmp(int i,int j){
    pii a=query[i],b=query[j];
    if((a.scd/chunk)!=(b.scd/chunk))return (a.scd/chunk)<(b.scd/chunk);
    else return a.fst<b.fst;
}

void solve(){
    memset(num,0,sizeof(num));
    int L=1,R=0;
    ll calcul=0ll;
    for(int i=1;i<=M;++i){
        int index=id[i];
        int Lb=query[index].fst,Rb=query[index].scd;
        while(L<Lb){
            calcul-=1ll*num[a[L]]*num[a[L]];
            num[a[L]]--;
            calcul+=1ll*num[a[L]]*num[a[L]];
            L++;
        }
        while(L>Lb){
            L--;
            calcul-=1ll*num[a[L]]*num[a[L]];
            num[a[L]]++;
            calcul+=1ll*num[a[L]]*num[a[L]]; 
        }
        while(R<Rb){
            R++;
            calcul-=1ll*num[a[R]]*num[a[R]];
            num[a[R]]++;
            calcul+=1ll*num[a[R]]*num[a[R]];
        }
        while(R>Rb){
            calcul-=1ll*num[a[R]]*num[a[R]];
            num[a[R]]--;
            calcul+=1ll*num[a[R]]*num[a[R]]; 
            R--;
        }
        ll A=calcul-1ll*(Rb-Lb+1);
        ll B=1ll*(Rb-Lb+1)*(Rb-Lb);
        ll C=gcd(A,B);
        ans[index]=mkp(A/C,B/C);
        //printf("%d ~ %d : %lld %lld
",L,R,A,B);
    }
}

int main(){
    while(~scanf("%d%d",&N,&M)){
        for(int i=1;i<=N;++i)
        scanf("%d",&a[i]);
        chunk=sqrt(N);
        //printf("%d is chunk of %d
",chunk,N);
        for(int i=1;i<=M;++i){
            id[i]=i;
            int u,v;
            scanf("%d%d",&u,&v);
            query[i]=mkp(u,v);
        }
        sort(id+1,id+1+M,cmp);
        //for(int i=1;i<=M;++i) printf("%d: %d~%d
",i,query[id[i]].fst,query[id[i]].scd);
        solve();
        for(int i=1;i<=M;++i){
            printf("%lld/%lld
",ans[i].fst,ans[i].scd);
        }    
    } 
    return 0;
}