Codeforces 847H

847H - Load Testing

思路：dp。

代码：

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define mem(a,b) memset(a,b,sizeof(a)

const int N=1e5+5;
ll dp[N]={0};
ll dp1[N]={0};
ll a[N];
ll t[N]={0};
ll t1[N]={0};
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin>>n;
    for(int i=1;i<=n;i++)cin>>a[i];
    
    t[1]=a[1];
    for(int i=2;i<=n;i++)
    {
        if(a[i]<=t[i-1])
        {
            dp[i]=dp[i-1]+t[i-1]-a[i]+1;
            t[i]=t[i-1]+1;
        }
        else 
        {
            t[i]=a[i];
            dp[i]=dp[i-1];
        }
    }
    
    t1[n]=a[n];
    for(int i=n-1;i>=1;i--)
    {
        if(a[i]<=t1[i+1])
        {
            dp1[i]=dp1[i+1]+t1[i+1]-a[i]+1;
            t1[i]=t1[i+1]+1;
        }
        else
        {
            t1[i]=a[i];
            dp1[i]=dp1[i+1];
        }
    }
    
    
    ll ans=min(dp1[1],dp[n]);
    for(int i=2;i<=n-1;i++)
    ans=min(ans,dp1[i]+dp[i]-min(t[i],t1[i])+a[i]); 
    
    cout<<ans<<endl;
    return 0;
}