HYSBZ - 2038 小Z的袜子(hose) (莫队)

中文题面

题解：莫队+组合数，注意LL啊啊啊

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <map>
#include <queue>
#include <vector>
#include <cstring>
#include <iomanip>
#include <set>
#include<ctime>
//CLOCKS_PER_SEC
#define se second
#define fi first
#define ll long long
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define Pii pair<int,int>
#define Pli pair<ll,int>
#define ull unsigned long long
#define pb push_back
#define fio ios::sync_with_stdio(false);cin.tie(0)
const int N=5e4+10;
const ull base=163;
const int INF=0x3f3f3f3f;
using namespace std;
int a[N];
struct node {
    int l,r,id;
}Q[N];
int pos[N];
int L=1,R=0;
ll ans=0;
pair<ll,ll>res[N];
int n,q;
ll mp[N];

bool cmp(node x,node y){
    if(pos[x.l]==pos[y.l])return x.r<y.r;
    return pos[x.l]<pos[y.l];
}
ll gcd(ll a,ll b){
    if(b==0)return a;
    else return gcd(b,a%b);
}
void del(int x){
    ans-=mp[a[x]]*(mp[a[x]]-1)/2;
    mp[a[x]]--;
    ans+=mp[a[x]]*(mp[a[x]]-1)/2;
}
void add(int x){
    ans-=mp[a[x]]*(mp[a[x]]-1)/2;
    mp[a[x]]++;
    ans+=mp[a[x]]*(mp[a[x]]-1)/2;
}
int main(){
    scanf("%d%d",&n,&q);
    int sz=sqrt(n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
        pos[i]=i/sz;
    }
    for(int i=1;i<=q;i++){
        scanf("%d%d",&Q[i].l,&Q[i].r);
        Q[i].id=i;
    }
    sort(Q+1,Q+1+q,cmp);
    for(int i=1;i<=q;i++){
        while(L>Q[i].l){
            L--;
            add(L);
        }
        while(L<Q[i].l){
            del(L);
            L++;
        }
       while(R<Q[i].r){
            R++;
            add(R);
        }
        while(R>Q[i].r){
            del(R);
            R--;
        }
        if(L==R){Q[i].l=0,Q[i].r=1;continue;}
        ll k=gcd(ans,1LL*(Q[i].r-Q[i].l+1)*(Q[i].r-Q[i].l)/2);
        res[Q[i].id].fi=ans/k;
        res[Q[i].id].se=1LL*(Q[i].r-Q[i].l+1)*(Q[i].r-Q[i].l)/2/k;
    }
    for(int i=1;i<=q;i++){
        printf("%lld/",res[i].fi);
        if(res[i].fi==0)printf("1\n");
        else printf("%lld\n",res[i].se);
    }
    return 0;
}