1062A - A Prank - CodeForces Solution

#include <bits/stdc++.h>
#define ll long long int
#define all(x) x.begin(), x.end()
#define pb push_back
#define sortall(x) sort(all(x))
#define seev(v,n) for(ll i=0;i<n;i++){ll x; cin>>x; v.pb(x);}
using namespace std;
typedef vector<int> vi; 
typedef vector<ll> vll;
const int MOD=1e9+7;
const ll INF=1e18;

void solve(){
int n;
cin>>n;
vi v;
seev(v,n);
int mx=0,c=1;
if(v[0]==1)c++;
for(int i=1;i<n;i++){
    if(v[i]-v[i-1]==1)
        c++;
    else{
        mx=max(mx,c);
        c=1;
    }
}
if(v[n-1]==1000)c++;
mx=max(mx,c);
if(mx<3)
    cout<<0;
else
    cout<<mx-2;
}

int main() {
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int t=1;
    // cin>>t;
    for (int i=1;i<=t;i++){
        solve();
    }
    return 0;
}