NC19913 [CQOI2009]中位数图

题目链接
题意：


题解：

AC代码

/*
    Author:zzugzx
    Lang:C++
    Blog:blog.csdn.net/qq_43756519
*/
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define endl '\n'
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int mod=1e9+7;
//const int mod=998244353;
const double eps = 1e-10;
const double pi=acos(-1.0);
const int maxn=1e6+10;
const ll inf=0x3f3f3f3f;
const int dir[4][2]={{0,1},{1,0},{0,-1},{-1,0}};

int a[maxn];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    int n,b;
    cin>>n>>b;
    map<int,int> m;
    int pos;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        if(a[i]==b)pos=i;
    }
    int sum=0,ans=1;
    m[0]++;
    for(int i=pos-1;i;i--){
        if(a[i]>b)sum--;
        else sum++;
        if(sum==0)ans++;
        m[sum]++;
    }
    sum=0;
    for(int i=pos+1;i<=n;i++){
        if(a[i]>b)sum--;
        else sum++;
        ans+=m[-sum];
    }
    cout<<ans;
    return 0;
}