Successive prime differences: Difference between revisions
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...for differences [6, 4, 2], there are 306 groups, where the first group = [31, 37, 41, 43] and the last group = [997141, 997147, 997151, 997153] |
...for differences [6, 4, 2], there are 306 groups, where the first group = [31, 37, 41, 43] and the last group = [997141, 997147, 997151, 997153] |
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</pre> |
</pre> |
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=={{header|Visual Basic .NET}}== |
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{{trans|Java}} |
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<lang vbnet>Imports System.Text |
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Module Module1 |
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Function Sieve(limit As Integer) As Integer() |
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Dim primes As New List(Of Integer) From {2} |
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Dim c(limit + 1) As Boolean REM composite = true |
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REM no need to process even numbers > 2 |
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Dim p = 3 |
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While True |
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Dim p2 = p * p |
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If p2 > limit Then |
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Exit While |
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End If |
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For i = p2 To limit Step 2 * p |
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c(i) = True |
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Next |
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Do |
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p += 2 |
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Loop While c(p) |
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End While |
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For i = 3 To limit Step 2 |
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If Not c(i) Then |
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primes.Add(i) |
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End If |
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Next |
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Return primes.ToArray |
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End Function |
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Function SuccessivePrimes(primes() As Integer, diffs() As Integer) As List(Of List(Of Integer)) |
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Dim results As New List(Of List(Of Integer)) |
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Dim dl = diffs.Length |
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Dim i = 0 |
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While i < primes.Length - dl |
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Dim group(dl) As Integer |
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group(0) = primes(i) |
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Dim j = i |
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While j < i + dl |
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If primes(j + 1) - primes(j) <> diffs(j - i) Then |
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GoTo outer REM continue the outermost loop |
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End If |
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group(j - i + 1) = primes(j + 1) |
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j += 1 |
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End While |
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results.Add(group.ToList) |
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outer: |
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i += 1 |
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End While |
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Return results |
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End Function |
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Function CollectionToString(Of T)(c As IEnumerable(Of T)) As String |
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Dim builder As New StringBuilder |
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builder.Append("[") |
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Dim it = c.GetEnumerator() |
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If it.MoveNext() Then |
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builder.Append(it.Current) |
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End If |
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While it.MoveNext() |
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builder.Append(", ") |
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builder.Append(it.Current) |
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End While |
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builder.Append("]") |
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Return builder.ToString |
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End Function |
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Sub Main() |
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Dim primes = Sieve(999999) |
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Dim diffsList = {({2}), ({1}), ({2, 2}), ({2, 4}), ({4, 2}), ({6, 4, 2})} |
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Console.WriteLine("For primes less than 1,000,000:-") |
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Console.WriteLine() |
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For Each diffs In diffsList |
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Console.WriteLine(" For differences of {0} ->", CollectionToString(diffs)) |
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Dim sp = SuccessivePrimes(primes, diffs) |
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If sp.Count = 0 Then |
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Console.WriteLine(" No groups found") |
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Continue For |
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End If |
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Console.WriteLine(" First group = {0}", CollectionToString(sp(0))) |
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Console.WriteLine(" Last group = {0}", CollectionToString(sp(sp.Count - 1))) |
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Console.WriteLine(" Number found = {0}", sp.Count) |
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Console.WriteLine() |
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Next |
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End Sub |
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End Module</lang> |
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{{out}} |
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<pre>For primes less than 1,000,000:- |
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For differences of [2] -> |
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First group = [3, 5] |
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Last group = [999959, 999961] |
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Number found = 8169 |
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For differences of [1] -> |
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First group = [2, 3] |
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Last group = [2, 3] |
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Number found = 1 |
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For differences of [2, 2] -> |
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First group = [3, 5, 7] |
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Last group = [3, 5, 7] |
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Number found = 1 |
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For differences of [2, 4] -> |
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First group = [5, 7, 11] |
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Last group = [999431, 999433, 999437] |
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Number found = 1393 |
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For differences of [4, 2] -> |
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First group = [7, 11, 13] |
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Last group = [997807, 997811, 997813] |
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Number found = 1444 |
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For differences of [6, 4, 2] -> |
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First group = [31, 37, 41, 43] |
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Last group = [997141, 997147, 997151, 997153] |
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Number found = 306</pre> |
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=={{header|Wren}}== |
=={{header|Wren}}== |
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