static object Solve()
{
var(n, k) = Read2();
var s = Console.ReadLine();
var cs = new char[k];
var q = new KeyedPriorityQueue <int, char>(i => s[i]);
for (int i = 0; i < n - k; i++)
{
q.Push(i);
}
var t = -1;
for (int i = n - k; i < n; i++)
{
q.Push(i);
while (q.Peek() < t)
{
q.Pop();
}
t = q.Pop();
cs[i - n + k] = s[t];
}
return(new string(cs));
}
public void Keyed_1()
{
var n = 100000;
var a = RandomHelper.CreateData(n);
var actual = new List <int>();
var q = new KeyedPriorityQueue <int, int>(x => x / 10);
foreach (var x in a)
{
q.Push(x);
}
while (q.Count > 0)
{
actual.Add(q.Pop());
}
var expected = a.OrderBy(x => x / 10).ToArray();
CollectionAssert.AreEqual(expected, actual);
actual.Clear();
q = new KeyedPriorityQueue <int, int>(x => x / 10, ComparerHelper <int> .Create(true));
foreach (var x in a)
{
q.Push(x);
}
while (q.Count > 0)
{
actual.Add(q.Pop());
}
expected = a.OrderByDescending(x => x / 10).ToArray();
CollectionAssert.AreEqual(expected, actual);
}