private static int GetLongestMonotoneSubsequenceLengthNaive <T>(IList <T> sequence, MonotoneType monotoneType) where T : IComparable <T>
{
int n = sequence.Count, res = 0;
var dp = new int[n];
for (int i = 0; i < n; i++)
{
dp[i] = 1;
for (int j = 0; j < i; j++)
{
switch (monotoneType)
{
case MonotoneType.Increasing:
if (sequence[i].CompareTo(sequence[j]) > 0)
{
dp[i] = Math.Max(dp[i], dp[j] + 1);
}
break;
case MonotoneType.Decreasing:
if (sequence[i].CompareTo(sequence[j]) < 0)
{
dp[i] = Math.Max(dp[i], dp[j] + 1);
}
break;
case MonotoneType.NonDecreasing:
if (sequence[i].CompareTo(sequence[j]) >= 0)
{
dp[i] = Math.Max(dp[i], dp[j] + 1);
}
break;
case MonotoneType.NonIncreasing:
if (sequence[i].CompareTo(sequence[j]) <= 0)
{
dp[i] = Math.Max(dp[i], dp[j] + 1);
}
break;
default:
throw new System.Exception("Unknown monotone type");
}
}
res = Math.Max(res, dp[i]);
}
return(res);
}
/// <summary>
/// Gets the length of the longest monotone subsequence with a given type of monotonicity
/// Time complexity: O(NlogN)
/// </summary>
public static int GetLongestMonotoneSubsequenceLength <T>(System.Collections.Generic.IEnumerable <T> sequence, MonotoneType monotoneType) where T : IComparable <T>
{
var minElements = new System.Collections.Generic.List <T>();
foreach (var element in sequence)
{
int l = -1, r = minElements.Count;
while (l + 1 < r)
{
int m = (l + r) / 2;
switch (monotoneType)
{
case MonotoneType.Increasing:
if (minElements[m].CompareTo(element) < 0)
{
l = m;
}
else
{
r = m;
}
break;
case MonotoneType.Decreasing:
if (minElements[m].CompareTo(element) > 0)
{
l = m;
}
else
{
r = m;
}
break;
case MonotoneType.NonDecreasing:
if (minElements[m].CompareTo(element) > 0)
{
r = m;
}
else
{
l = m;
}
break;
case MonotoneType.NonIncreasing:
if (minElements[m].CompareTo(element) < 0)
{
r = m;
}
else
{
l = m;
}
break;
default:
throw new System.Exception("Unknown monotone type");
}
}
if (r == minElements.Count)
{
minElements.Add(element);
}
else
{
minElements[r] = element;
}
}
return(minElements.Count);
}
void DoMonotoneTest(MonotoneType monotoneType)
{
int n = 8;
var p = PermutationUtils.First(n);
do
{
var copyP = (int[])p.Clone();
var my = SequenceUtils.GetLongestMonotoneSubsequenceLength(copyP, monotoneType);
Assert.IsTrue(p.SequenceEqual(copyP));
var correct = GetLongestMonotoneSubsequenceLengthNaive(p, monotoneType);
Assert.AreEqual(correct, my);
var mlist = SequenceUtils.GetLongestMonotoneSubsequence(copyP, monotoneType);
Assert.IsTrue(p.SequenceEqual(copyP));
Assert.AreEqual(my, mlist.Length);
for (int i = 1; i < mlist.Length; ++i)
{
Assert.IsTrue(mlist[i] >= 0 && mlist[i] < n);
Assert.IsTrue(mlist[i] > mlist[i - 1]);
switch (monotoneType)
{
case MonotoneType.Increasing:
Assert.IsTrue(p[mlist[i]] > p[mlist[i - 1]]);
break;
case MonotoneType.Decreasing:
Assert.IsTrue(p[mlist[i]] < p[mlist[i - 1]]);
break;
case MonotoneType.NonDecreasing:
Assert.IsTrue(p[mlist[i]] >= p[mlist[i - 1]]);
break;
case MonotoneType.NonIncreasing:
Assert.IsTrue(p[mlist[i]] <= p[mlist[i - 1]]);
break;
default:
throw new System.Exception("Unknown monotone type");
}
}
} while (PermutationUtils.Next(p));
var rnd = new Random(123);
for (int times = 0; times < 100; ++times)
{
n = rnd.Next(50) + 10;
p = new int[n];
for (int i = 0; i < n; i++)
{
p[i] = rnd.Next(20);
}
var correct = GetLongestMonotoneSubsequenceLengthNaive(p, monotoneType);
var my = GetLongestMonotoneSubsequenceLengthNaive(p, monotoneType);
Assert.AreEqual(correct, my);
n = 8;
p = new int[n];
for (int i = 0; i < n; i++)
{
p[i] = rnd.Next(5);
}
Array.Sort(p);
do
{
correct = GetLongestMonotoneSubsequenceLengthNaive(p, monotoneType);
my = GetLongestMonotoneSubsequenceLengthNaive(p, monotoneType);
Assert.AreEqual(correct, my);
} while (PermutationUtils.Next(p));
}
}
/// <summary>
/// Gets the longest monotone subsequence with a given type of monotonicity
/// Returns not the subsequence itself, but the sequence of positions of elements.
/// Time complexity: O(NlogN)
///
/// WARNING: Allocates additional O(N) space
/// </summary>
public static int[] GetLongestMonotoneSubsequence <T>(System.Collections.Generic.IList <T> sequence, MonotoneType monotoneType) where T : IComparable <T>
{
var prev = new int[sequence.Count];
var minElements = new System.Collections.Generic.List <T>();
var minElementsPositions = new System.Collections.Generic.List <int>();
for (int i = 0; i < sequence.Count; ++i)
{
var element = sequence[i];
int l = -1, r = minElements.Count;
while (l + 1 < r)
{
int m = (l + r) / 2;
switch (monotoneType)
{
case MonotoneType.Increasing:
if (minElements[m].CompareTo(element) < 0)
{
l = m;
}
else
{
r = m;
}
break;
case MonotoneType.Decreasing:
if (minElements[m].CompareTo(element) > 0)
{
l = m;
}
else
{
r = m;
}
break;
case MonotoneType.NonDecreasing:
if (minElements[m].CompareTo(element) > 0)
{
r = m;
}
else
{
l = m;
}
break;
case MonotoneType.NonIncreasing:
if (minElements[m].CompareTo(element) < 0)
{
r = m;
}
else
{
l = m;
}
break;
default:
throw new System.Exception("Unknown monotone type");
}
}
if (r == minElements.Count)
{
minElements.Add(element);
minElementsPositions.Add(i);
}
else
{
minElements[r] = element;
minElementsPositions[r] = i;
}
if (r > 0)
{
prev[i] = minElementsPositions[r - 1];
}
else
{
prev[i] = -1;
}
}
var ans = new int[minElements.Count];
int curPosition = minElementsPositions[minElementsPositions.Count - 1], curLength = minElements.Count;
while (curPosition != -1)
{
ans[--curLength] = curPosition;
curPosition = prev[curPosition];
}
return(ans);
}