3508. 【NOIP2013模拟11.5B组】好元素(good) 
(File IO): input:good.in output:good.out

Goto ProblemSet

 #include <cstdio>

 #include <cstring>

 #include <string>

 #include <iostream>

 #include <algorithm>

 #define N 5007

 #define mo 14150547

 #define z 2000000000

 #define LL long long

 using namespace std;

 LL n, a[N], h[mo + ];

 int ans;

 bool f;

 LL hash(LL x)

 {

     LL p = x % mo;

     while (h[p] !=  && h[p] != x - z && p <= mo)    p = (p + ) % mo;

     return p;

 }

 void work()

 {

     for (int i = ; i <= n; i++)

     {

         for (int j = ; j < i; j++)

             if (h[hash(a[i] - a[j] + z)] == a[i] - a[j] && a[i] - a[j] != )

             {

                 ans++;

                 break;

             }

             else if (a[i] - a[j] == )

             {

                 if (f)

                 {

                     ans++;

                     break;

                 }

             }

         for (int j = ; j <= i; j++)

         {

             LL p = (a[i] + a[j] + z) % mo;

             while (h[p] != a[i] + a[j] && h[p] !=  && p <= mo)    p = (p + ) % mo;

             if (a[i] + a[j] != )    h[p] = a[i] + a[j];

             else f = true;

         }

     }

 }

 int main()

 {

     freopen("good.in", "r", stdin);

     freopen("good.out", "w", stdout);

     scanf("%lld", &n);

     for (int i = ; i <= n; i++)

         scanf("%lld", &a[i]);

     work();

     cout << ans;

 }