双指针代码

//双指针
#include
#include
using namespace std;
using ll = long long;
const int N = 2e5 + 9;
int a[N], c[N];
 
void slove()
{
	int n; cin >> n;
	for (int i = 1; i <= n; ++i) cin >> a[i];
	//将需要用到的桶重置为0
	for (int i = 1; i <= n; ++i) c[a[i]] = 0;
 
	ll ans = 0;
	for (int i = 1, j = 0; i <= n; ++i)
	{
		//向右寻找j+1
		while (j < n && !c[a[j + 1]]) c[a[++j]]++;
		//更新答案
		ans = max(ans, j - i + 1ll);
		c[a[i]]--;//j+1重复 i向右移动
	}
 
	cout << ans << '\n';
}
 
 
int main()
{
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int t; cin >> t;
	while (t--) slove();
	return 0;
}