BZOJ1303 [CQOI2009]中位数图

 1 #include <cstdio>
 2 #include <map>
 3 using namespace std;
 4 typedef long long LL;
 5 int a[100005];
 6 map<int,int>mp;
 7 int main(){
 8     int n,m,pos;scanf("%d%d",&n,&m);
 9     for(int i = 1;i<=n;++i){
10         scanf("%d",&a[i]);
11         if(a[i]==m)pos = i;
12     }
13     int x = 0,y = 0;
14     for(int i = pos+1;i<=n;++i){
15         if(a[i]>m)x++;
16         else y++;
17         mp[x-y]++;
18     }
19     if(pos==1){printf("%d\n",mp[0]+1);return 0;}
20     LL ans = mp[0];
21     x = 0;y = 0;
22     for(int i = pos-1;i>=1;--i){
23         if(a[i]>m)x++;
24         else y++;
25         if(x==y)ans++;
26        // printf("i=%d %d\n",i,mp[y-x]);
27         ans+=mp[y-x];
28     }
29     printf("%lld\n",ans+1);
30     return 0;
31 }