1491C - Pekora and Trampoline - CodeForces Solution

#include <bits/stdc++.h>
#define fori(i,a,b) for(int i = a;i <= b;i ++)
#define fore(i,a,b) for(int i = a;i >= b;i --)
#define pii pair<int,int>
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define bit(n,i) ((n >> i) & 1)
using namespace std;
typedef long long ll;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int l,int r)
{
    return l + rng() % (r - l + 1);
}
int const N = 2e5 + 10;
int a[N],dp[N];
void speed()
{
	ios_base::sync_with_stdio(NULL);
	cin.tie(NULL);
	cout.tie(NULL);
}
int t,n;
void solve()
{
    cin >> n;
    fori(i,1,n)
    {
        cin >> a[i];
        dp[i] = 0;
    }
    ll res(0);
    fori(i,1,n)
    {
        ll c = a[i] - dp[i] - 1;
        res += max(0ll,c);
        for(int j = i + 2;j <= min(n,a[i] + i);j ++)
        dp[j] += 1;
        if(i < n and c < 0) dp[i + 1] -= c;
    }
    cout << res;
}
int main()
{
    if(fopen("task.inp","r"))
    {
        freopen("task.inp","r",stdin);
        freopen("task.out","w",stdout);
    }
    cin >> t;
    while(t--)
    {
        solve();
        cout << "\n";
    }
    return 0;
}