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Cod sursa(job #543429)
#include <stdio.h>
#include <vector>
using namespace std;
struct sp
{
int s1,s2,s;
};
vector <sp> h[21001];
sp aux;
int n,v[1025],sol;
inline bool comp(int i,int j,int k,int l)
{
if (h[i][j].s1==h[k][l].s1) return 0;
if (h[i][j].s1==h[k][l].s2) return 0;
if (h[i][j].s2==h[k][l].s1) return 0;
if (h[i][j].s2==h[k][l].s2) return 0;
return 1;
}
int main()
{
int i,j,k,l,a,l2;
freopen("oite.in","r",stdin);
freopen("oite.out","w",stdout);
scanf("%d%d",&n,&l);
for (i=1;i<=n;++i)
scanf("%d",&v[i]);
for (i=1;i<=n;++i)
for (j=i+1;j<=n;++j)
if (i!=j)
{
aux.s1=i;
aux.s2=j;
aux.s=v[i]+v[j];
h[aux.s%21001].push_back(aux);
}
l2=l%21001;
for (i=0;i<=(l2+1)/2;++i)
for (j=0;j<h[i].size();++j)
{
a=l2-i;
if (a<0) a+=21001;
for (k=0;k<h[a].size();++k)
if ((h[i][j].s+h[a][k].s==l)&&(comp(i,j,a,k)))
++sol;
}
for (i=21001-(21001-l2)/2;i<21001;++i)
for (j=0;j<h[i].size();++j)
{
a=l2-i;
if (a<0) a+=21001;
for (k=0;k<h[a].size();++k)
if ((h[i][j].s+h[a][k].s==l)&&(comp(i,j,a,k)))
++sol;
}
printf("%d",sol/3);
return 0;
}