二次聯通門 : BZOJ 1303: [CQOI2009]中位數圖

/*
    BZOJ 1303: [CQOI2009]中位數圖
    
    對於一個數
    若當前數大於中位數，則記為1
    小於中位數，記為-1，等於則記為0

    對原數列做一個前綴和

    觀察發現，若一段區間符合要求
    則該段區間內大於中位數的數的數量等於小於中位數的
    那麽統計一下每個前綴和出現的次數就好了
    
*/
#include <cstdio>
#include <iostream>

const int BUF = 12312313;
char
 
 Buf[BUF], *buf = Buf;

inline void read (int &now)
{
    for (now = 0; !isdigit (*buf); ++ buf);
    for (; isdigit (*buf); now = now * 10 + *buf - ‘0‘, ++ buf);
}
#define Max 100002
int c[Max], s[Max];
short fc[Max], zc[Max];

int Main ()
{
    fread (buf, 1, BUF, stdin); int N, B; read (N), read (B);
    register 
 
int i, j; int x, p = -1, Answer = 0;
    for (i = 1; i <= N; ++ i) 
    {
        read (x); s[i] = s[i - 1];
        if (x > B) ++ s[i];    else if (x < B) -- s[i]; else p = i;
        if (p == -1) s[i] < 0 ? ++ fc[- s[i]] : ++ zc[s[i]];    
    }
    for (++ zc[0]; p <= N; ++ p) Answer += s[p] < 0
 
 ? fc[- s[p]] : zc[s[p]];
    printf ("%d", Answer);    
    return 0;
}
int ZlycerQan = Main ();
int main (int argc, char *argv[]) {;}

BZOJ 1303: [CQOI2009]中位數圖