Shared code

#include <bits/stdc++.h>
#define mod 1000000007;
#define ll long long
using namespace std;
 
int main()
{
	ll n;
	cin >> n;
	ll arr[n];
	for (int i = 0; i < n; ++i)
	{
		cin >> arr[i];
	}
	ll ans = 0;
	ll start = 0, end = 0;
	unordered_set<ll> set;
	while (end < n )
	{
		if (set.find(arr[end]) == set.end())
		{
			set.insert(arr[end]);
			ans = max(ans, end - start + 1);
			end++;
		}
		else
		{
			set.erase(arr[start]);
			start++;
		}
	}
	cout << ans;
 
	return 0;
}