【uoj122】 NOI2013—树的计数

// uoj122
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define inf (1ll<<30)
#define MOD 1000000007
#define Pi acos(-1.0)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

const int maxn=200010;
int vis[maxn],dfn[maxn],bfn[maxn],t[maxn],pos[maxn],n;
double ans;

int main() {
	scanf("%d",&n);
	for (int i=1;i<=n;i++) scanf("%d",&dfn[i]);
	for (int i=1;i<=n;i++) scanf("%d",&bfn[i]),t[bfn[i]]=i;
	for (int i=1;i<=n;i++) dfn[i]=t[dfn[i]];
	for (int i=1;i<=n;i++) pos[dfn[i]]=i;
	ans=2;
	int l=2,r=n+1;
	vis[1]=1,vis[2]=1;
	for (int i=3;i<=n;i++) {
		if (pos[i-1]>pos[i]) ans++;
		if (pos[i-1]+1==pos[i] && r-l-1==n-i+1) ans+=0.5;
		vis[pos[i]]=1;
		while (vis[l+1]) l++;
		while (vis[r-1]) r--;
	}
	printf("%.3lf",ans);
	return 0;
}