大视野2038 小z的袜子 莫队算法

[code]#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstring>
using namespace std;
#define LL long long 
int n,m;
int a[500005];

struct node{
    int l,r;
    int id;
}Q[500005];
LL gcd(LL a,LL b){
    return b==0?a:gcd(b,a%b);
}
struct q{
    LL  a,b;
    void huajian(){
        LL d = gcd(a,b);
        a /= d;
        b /= d; 
    }
}ans[500005];
int num[500005];
int Un;
bool cmp(node a,node b){
    if(a.l/Un != b.l/Un) return a.l/Un < b.l/Un;
    else return a.r < b.r;
}
void work(){
    LL temp = 0;
    memset(num,0,sizeof(num));
    int l = 1;
    int r = 0;
    for(int i = 0;i < m;i++){
        while(r < Q[i].r){
            r ++;
            temp -= (LL) num[a[r]] * num[a[r]];
            num[a[r]] ++;
            temp += (LL) num[a[r]] * num[a[r]];
        }
        while(r > Q[i].r){
            temp -= (LL) num[a[r]] * num[a[r]];
            num[a[r]] --;
            temp += (LL) num[a[r]] * num[a[r]];
            r--; 
        }
        while(l < Q[i].l){
            temp -= (LL) num[a[l]] * num[a[l]];
            num[a[l]] --;
            temp += (LL) num[a[l]] * num[a[l]];
            l++;
        }
        while(l > Q[i].l){
            l --;
            temp -= (LL) num[a[l]] * num[a[l]];
            num[a[l]] ++;
            temp += (LL) num[a[l]] * num[a[l]];
        }
        ans[Q[i].id].a = temp - (r-l+1);
        ans[Q[i].id].b = (LL)(r-l+1)*(r-l);
        ans[Q[i].id].huajian();
    }
}

int main(){

    while(cin >> n >> m){
        for(int i = 1;i <= n;i++){
            scanf("%d",&a[i]);
        }       
        for(int i = 0;i < m;i++){
            int x,y;
            scanf("%d%d",&x,&y);
            Q[i].l = x;
            Q[i].r = y;
            Q[i].id = i;
        }
        Un = (int)sqrt(n);
        sort(Q,Q+m,cmp);
        work();
        for(int i = 0;i < m;i++){
            printf("%lld/%lld\n",ans[i].a,ans[i].b);
        }
    }
    return 0;
}