P2421 A-B数对（增强版）

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#define in long long
#define mo 20047
#define mo2 13831
using namespace std;
struct node
{
    in cs;
    in next;
    in to;
}edge[2000001];
in ans,tot,head[2000001],a[200001],i,j,n,c,b;
in qr()
{
    in x=1,f=0;
    char ch=getchar();
    while(ch<‘0‘||ch>‘9‘)
    {
        if(ch==‘-‘) x=-1;
        ch=getchar();
    }
    while(ch>=‘0‘&&ch<=‘9‘)
    {
        f=f*10+(in)ch-48;
        ch=getchar();
    }
    return x*f;
}
in get_hash1(in k)
{
    return k*1007%mo;
}
in get_hash2(in q)
{
    return q*1009%mo2;
}
void lj(in from,in to)
{ 
    for(int l=head[from];l;l=edge[l].next)
    {
        if(edge[l].to==to)
        {
            edge[l].cs++;
            return;
        }
    }
     tot++;
    edge[tot].next=head[from];
    edge[tot].to=to;
    head[from]=tot;
    edge[tot].cs++;
}
void add(in u,in v)
{
    if(head[u])
    lj(u,v);
    else
    {
        tot++;
        edge[tot].next=head[u];
        edge[tot].to=v;
        head[u]=tot;
        edge[tot].cs++;
    }
}
int query(in u,in v)
{
    for(j=head[u];j;j=edge[j].next)
    {
        if(edge[j].to==v)
        return edge[j].cs;
    }
    return 0;
}
int main()
{
    n=qr();c=qr();
    for(i=0;i<n;++i)
    {
        a[i]=qr();
        in x=get_hash1(a[i]);
        in y=get_hash2(a[i]);
        add(x,y);
    }
    for(i=0;i<n;++i)
    {
        b=c+a[i];
        in y=get_hash1(b);
        in z=get_hash2(b);
        ans+=query(y,z);
    }
    cout<<ans;
    return 0;
}