蹄球锦标赛

 https://ac.nowcoder.com/acm/contest/918/A

思路：判断每个环，肯定左或右有传的，也可能两边都要传的；

#include<algorithm>
#include<set>
#include<queue>
#include<cmath>
#include<cstring>
#include<iostream>
#include<set>
#include<vector>
#include<queue>
#include<cmath>
#include<cstdio>
#include<map>
#include<stack>
#include<string>
#include<bits/stdc++.h>
using namespace std;

#define sfi(i) scanf("%d",&i)
#define sfs(i) scanf("%s",(i))
#define pri(i) printf("%d\n",i)
#define sff(i) scanf("%lf",&i)
#define ll long long
#define ull unsigned long long
#define mem(x,y) memset(x,y,sizeof(x))
#define INF 0x3f3f3f3f
#define eps 1e-16
#define PI acos(-1)
#define lowbit(x) ((x)&(-x))
#define zero(x) (((x)>0?(x):-(x))<eps)
#define fl() printf("flag\n")
#define MOD(x) ((x%mod)+mod)%mod
#define endl '\n'
#define pb push_back
#define lson rt<<1,l,mid
#define rson rt<<1|1,mid+1,r
#define FAST_IO ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)

const int maxn=2e6+9;
const int mod=1e9+7;

inline ll read()
{
    ll f=1,x=0;
    char ss=getchar();
    while(ss<'0'||ss>'9')
    {
        if(ss=='-')f=-1;ss=getchar();
    }
    while(ss>='0'&&ss<='9')
    {
        x=x*10+ss-'0';ss=getchar();
    }    return f*x;
}

int a[maxn],p[maxn];
int main()
{
    //FAST_IO;
    //freopen("input.txt","r",stdin);


    int n;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
    }
    sort(a+1,a+n+1);

    p[0]=-1;
    p[1]=1;
    p[n]=-1;
    p[n+1]=1;

    for(int i=2;i<n;i++)
    {
        if(a[i]-a[i-1]==a[i+1]-a[i])
        {
            p[i]=-1;
        }
        else if(a[i]-a[i-1]>a[i+1]-a[i])
        {
            p[i]=1;
        }
        else p[i]=-1;
    }
    int ans=0;
    for(int i=1;i<=n;i++)
    {
        if(p[i]==1&&p[i+1]==-1)
        {
            ans++;
            if(p[i-1]==1&&p[i+2]==-1) ans++;
        }
    }
    cout<<ans<<endl;

}