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Cod sursa(job #497076)
#include <cstdio>
#include <algorithm>
#include <list>
#include <vector>
using namespace std;
#define Nmax 1030
#define MOD 666013
int n, L;
int v[Nmax];
list < pair <int, int> > H[MOD + 10];
void citire () {
int i;
scanf ("%d %d", &n, &L);
for (i = 1; i <= n; i++)
scanf ("%d", &v[i]);
}
void insert (int val) {
int p = val % MOD;
for (list < pair <int, int> >::iterator it = H[p].begin (); it != H[p].end (); it++)
if (it->first == val) it->second++;
H[p].push_back (make_pair(val, 1));
}
void erase (int val) {
int p = val % MOD;
for (list < pair <int, int> >::iterator it = H[p].begin (); it != H[p].end (); it++) {
if (it->first == val) {
it->second--;
//if (it->second == 0)
// H[p].erase (it);
return ;
}
}
}
int find (int val) {
int p = val % MOD;
for (list < pair <int, int> >::iterator it = H[p].begin (); it != H[p].end (); it++) {
if (it->first == val)
return it->second;
}
return 0;
}
void rezolva () {
int i, j, nr = 0;
for (i = 2; i < n; i++)
for (j = i + 1; j <= n; j++)
insert (v[i] + v[j]);
for (i = 2; i < n; i++) {
for (j = i + 1; j <= n; j++)
erase (v[i] + v[j]);
for (j = i - 1; j >= 1; j--)
if(L >= v[i] + v[j]) {
nr+= find (L - v[i] - v[j]);
}
}
printf ("%d", nr);
}
int main () {
freopen ("oite.in", "r", stdin);
freopen ("oite.out", "w", stdout);
citire ();
rezolva ();
return 0;
}