二次联通门 : 

 

 

 

 

/*    BZOJ 1800: [Ahoi2009]fly 飞行棋    乱搞一下就好*/#include 
     
      #include 
      
       #define rg registerinline void read (int &n){    rg int c = getchar ();    for (n = 0; !isdigit (c); c = getchar ());    for (; isdigit (c); n = n * 10 + c - '0', c = getchar ());}#define Max 1000001int c[Max]; bool is[Max];int main (int argc, char *argv[]){    int N, x, s = 0, Answer = 0; rg int i, j; read (N);    for (i = 1; i <= N; ++ i)         read (x), is[s] = true, c[i] = s, s += x;    for (i = 1; i <= N; ++ i)        for (j = i + 1; j <= N; ++ j)             if (is[c[j] + (s - 2 * (c[j] - c[i])) / 2] && is[c[j] + (s - 2 * (c[j] - c[i])) / 2 + c[j] - c[i]]) ++ Answer;    printf ("%d", Answer); return 0;}