public static void Run()
{
using (FastScanner fs = new FastScanner(new BufferedStream(Console.OpenStandardInput())))
using (StreamWriter writer = new StreamWriter(new BufferedStream(Console.OpenStandardOutput())))
{
int n = fs.NextInt();
int[] a = Array.ConvertAll(fs.ReadLine().Split(), Convert.ToInt32);
SumSegmentTree seg = new SumSegmentTree(new long[n + 1]);
double expDiff = 0, denom = n * 1L * (n + 1) / 2, expInvCount = 0;
long inv = 0;
for (int i = n - 1; i >= 0; i--)
{
inv += seg.QuerySum(0, a[i] - 1);
expInvCount += ExpectedInverseCount(n - i);
expDiff += (expInvCount - inv) / denom;
seg.Update(a[i], n - i);
}
long initialInverseCount = 0;
seg = new SumSegmentTree(new long[n + 1]);
for (int i = n - 1; i >= 0; i--)
{
initialInverseCount += seg.QuerySum(0, a[i] - 1);
seg.Update(a[i], 1);
}
writer.WriteLine((initialInverseCount + expDiff).ToString().Replace(",", "."));
}
}
public void CanUpdateValue()
{
var sut = new SumSegmentTree(new[] { 1, 3, 5, 7, 9, 11 });
Assert.Equal(15, sut.GetSegmentValue(1, 3));
sut.Update(2, 10);
Assert.Equal(20, sut.GetSegmentValue(1, 3));
}
public static void Run()
{
using (FastScanner fs = new FastScanner(new BufferedStream(Console.OpenStandardInput())))
using (StreamWriter writer = new StreamWriter(new BufferedStream(Console.OpenStandardOutput())))
{
int n = fs.NextInt(), q = fs.NextInt();
LinkedList<int>[] apps = new LinkedList<int>[n];
SumSegmentTree seg = new SumSegmentTree(new int[q]);
for (int i = 0; i < n; i++)
{
apps[i] = new LinkedList<int>();
}
int last = 0, j = 0;
for (int i = 0; i < q; i++)
{
int t = fs.NextInt(), x = fs.NextInt();
if (t == 1)
{
x--;
apps[x].AddLast(j);
seg.Update(j, j, 1);
j++;
}
else if (t == 2)
{
x--;
foreach (int notif in apps[x])
{
seg.Update(notif, notif, 0);
}
apps[x].Clear();
}
else
{
if (x > last)
{
last = x;
seg.Update(0, x - 1, 0);
}
}
writer.WriteLine(seg.QuerySum(0, q - 1));
writer.Flush();
}
}
}
public void CanConstructSegmentTreeFromArray()
{
var sut = new SumSegmentTree(new[] { 1, 3, 5, 7, 9, 11 });
}
public void CanGetSum()
{
var sut = new SumSegmentTree(new[] { 1, 3, 5, 7, 9, 11 });
Assert.Equal(15, sut.GetSegmentValue(1, 3));
}