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Cod sursa(job #75968)
#include <cstdio>
#include <vector>
using namespace std;
#define maxn 1024
#define maxp 666013
FILE *in = fopen("oite.in", "r"), *out = fopen("oite.out", "w");
struct hash
{
int i, j;
};
int n;
int L;
int a[maxn];
//hash *h[maxp] = {NULL};
vector<hash> h[maxp];
void hadd(int p, int q)
{
int t = (a[p] + a[q]) % maxp;
hash tt;
tt.i = p;
tt.j = q;
h[t].push_back(tt);
}
int hget(int p, int q)
{
int s = 0;
if ( L - (a[p] + a[q]) < 0 )
return 0;
int t = (L - (a[p] + a[q])) % maxp;
for ( vector<hash>::iterator i = h[t].begin(); i != h[t].end(); ++i )
if ( (*i).i > q )
++s;
return s;
}
int main()
{
fscanf(in, "%d %d", &n, &L);
for ( int i = 0; i < n; ++i )
fscanf(in, "%d", &a[i]);
for ( int i = 0; i < n; ++i )
for ( int j = i+1; j < n; ++j )
hadd(i, j);
int cnt = 0;
for ( int i = 0; i < n; ++i )
for ( int j = i+1; j < n; ++j )
cnt += hget(i, j);
fprintf(out, "%d\n", cnt);
return 0;
}