1626C - Monsters And Spells - CodeForces Solution

#include<bits/stdc++.h>
using namespace std;
const int N=110;
#define int long long
int t,n,k[N],h[N];

signed main(){
	cin>>t;
	while(t--){
		cin>>n;
		for(int i=1;i<=n;i++) cin>>k[i];
		for(int i=1;i<=n;i++) cin>>h[i];
		
		int ans=0,last=n;
		
		for(int i=n;i>=1;i--){
			if(k[i]-k[i-1]>=h[i]){
				int pos=k[i]-h[i];
				ans += (k[last]-pos+1)*(k[last]-pos)/2;
				last=i-1;
			}
			else{
				h[i-1]=max(h[i-1],h[i]-(k[i]-k[i-1]));
			}
		}
		cout<<ans<<endl;
	}
}