[C++] bzoj 1303: [CQOI2009]中位数图 数学

//qscqesze
#include <cstdio>
#include <cmath>
#include <cstring>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <set>
#include <vector>
#include <sstream>
#include <queue>
#include <typeinfo>
#include <fstream>
#include <map>
#include <stack>
typedef long long ll;
using namespace std;
//freopen("D.in","r",stdin);
//freopen("D.out","w",stdout);
#define sspeed ios_base::sync_with_stdio(0);cin.tie(0)
#define maxn 1000001
#define mod 10007
#define eps 1e-9
int Num;
char CH[20];
//const int inf=0x7fffffff;   //нчоч╢С
const int inf=0x3f3f3f3f;
/*
inline void P(int x)
{
  Num=0;if(!x){putchar('0');puts("");return;}
  while(x>0)CH[++Num]=x%10,x/=10;
  while(Num)putchar(CH[Num--]+48);
  puts("");
}
*/
inline ll read()
{
  int x=0,f=1;char ch=getchar();
  while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
  while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
  return x*f;
}
inline void P(int x)
{
  Num=0;if(!x){putchar('0');puts("");return;}
  while(x>0)CH[++Num]=x%10,x/=10;
  while(Num)putchar(CH[Num--]+48);
  puts("");
}
//**************************************************************************************
int num[maxn];
int sum[maxn];
int l[maxn],r[maxn];
int point;
int main()
{
  int n,b;
  scanf("%d%d",&n,&b);
  for(int i=1;i<=n;i++)
  {
    scanf("%d",&num[i]);
    if(num[i]==b)
      point=i;
    if(num[i]>b)
      num[i]=1;
    else if(num[i]<b)
      num[i]=-1;
    else
      num[i]=0;
  }
  l[n]=1,r[n]=1;
  for(int i=point-1;i>=1;i--)
  {
    sum[i]=sum[i+1]+num[i];
    l[sum[i]+n]++;
  }
  for(int i=point+1;i<=n;i++)
  {
    sum[i]=sum[i-1]+num[i];
    r[sum[i]+n]++;
  }
  int ans=0;
  for(int i=0;i<=2*n;i++)
  {
    ans+=l[i]*r[2*n-i];
  }
  cout<<ans<<endl;
}