//https://en.wikipedia.org/wiki/Patience_sorting
public static int[] LASIndices(IReadOnlyList <int> sequence)
{
;
if (sequence.Count == 0)
{
return(new int[0]);
}
var pileTops = new List <LCANode> {
new LCANode(0, null)
};
for (int i = 1; i < sequence.Count; i++)
{
int v = sequence[i];
//binary search for the first pileTop > v
int a = 0;
int b = pileTops.Count;
while (a != b)
{
int c = (a + b) / 2;
if (sequence[pileTops[c].value] > v)
{
b = c;
}
else
{
a = c + 1;
}
}
if (a < pileTops.Count)
{
pileTops[a] = new LCANode(i, a > 0 ? pileTops[a - 1] : null);
}
else
{
pileTops.Add(new LCANode(i, pileTops[a - 1]));
}
}
//follow pointers back through path
var las = new int[pileTops.Count];
int j = pileTops.Count - 1;
for (var node = pileTops[j]; node != null; node = node.prev)
{
las[j--] = node.value;
}
return(las);
}
public LCANode(int value, LCANode prev)
{
this.value = value;
this.prev = prev;
}
