CodeForces - 1463D
90nwyn
2020-12-18 10:16:24
[题目链接](https://vjudge.net/problem/CodeForces-1463D)
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```cpp
#include <bits/stdc++.h>
using namespace std;
const int M=4e5+5;
int n,a[M],b[M];
int main()
{
int T;scanf("%d",&T);
while(T--)
{
scanf("%d",&n);
for(int i=1;i<=2*n;i++)b[i]=0;
for(int i=1;i<=n;i++)
{
scanf("%d",&a[i]);
b[a[i]]=1;
}
int l=0,r=0;
for(int i=1,j=1;i<=n;i++)
{
j=max(j,a[i]);
while(j<=2*n&&b[j])j++;
if(j>2*n)break;
l++;j++;
}
for(int i=n,j=2*n;i>=1;i--)
{
j=min(j,a[i]);
while(j>=1&&b[j])j--;
if(j<1)break;
r++;j--;
}
printf("%d\n",l-(n-r)+1);
}
return 0;
}
```