蒟蒻求助

# include<bits/stdc++.h>
using namespace std;

int l[10005],r[10005];
int n,len,ans,ansn;

int main()
{
    cin>>n;
    for (int i=1;i<=n;i++) l[i]=10005;
    for (int i=1;i<=n;i++){
        int x;
        cin>>x;
        l[x]=min(i,l[x]);
        r[x]=max(i,r[x]);
        len=max(len,x);
        ansn=ansn+x;
    }
    for (int i=len-1;i>=1;i--){
        l[i]=min(l[i+1],l[i]);
        r[i]=max(r[i+1],r[i]);
    } 
    for (int i=1;i<=len;i++)
        if (l[i]<=r[i]) ans=ans+(r[i]-l[i]+1);
    ans=ans-ansn;
    cout<<ans;
    return 0;
}