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Task/Truncatable-primes/PureBasic/truncatable-primes-1.purebasic

@@ -0,0 +1,68 @@
+#MaxLim = 999999
+
+Procedure is_Prime(n)
+  If     n<=1 : ProcedureReturn #False
+  ElseIf n<4  : ProcedureReturn #True
+  ElseIf n%2=0: ProcedureReturn #False
+  ElseIf n<9  : ProcedureReturn #True
+  ElseIf n%3=0: ProcedureReturn #False
+  Else
+    Protected r=Round(Sqr(n),#PB_Round_Down)
+    Protected f=5
+    While f<=r
+      If n%f=0 Or n%(f+2)=0
+        ProcedureReturn #False
+      EndIf
+      f+6
+    Wend
+  EndIf
+  ProcedureReturn #True
+EndProcedure
+
+Procedure TruncateLeft(n)
+  Protected s.s=Str(n), l=Len(s)-1
+  If Not FindString(s,"0",1)
+    While l>0
+      s=Right(s,l)
+      If Not is_Prime(Val(s))
+        ProcedureReturn #False
+      EndIf
+      l-1
+    Wend
+    ProcedureReturn #True
+  EndIf
+EndProcedure
+
+Procedure TruncateRight(a)
+  Repeat
+    a/10
+    If Not a
+      Break
+    ElseIf Not is_Prime(a) Or a%10=0
+      ProcedureReturn #False
+    EndIf
+  ForEver
+  ProcedureReturn #True
+EndProcedure
+
+i=#MaxLim
+Repeat
+  If is_Prime(i)
+    If Not truncateleft And TruncateLeft(i)
+      truncateleft=i
+    EndIf
+    If Not truncateright And TruncateRight(i)
+      truncateright=i
+    EndIf
+  EndIf
+  If truncateleft And truncateright
+    Break
+  Else
+    i-2
+  EndIf
+Until i<=0
+
+x.s="Largest TruncateLeft= "+Str(truncateleft)
+y.s="Largest TruncateRight= "+Str(truncateright)
+
+MessageRequester("Truncatable primes",x+#CRLF$+y)

Task/Truncatable-primes/PureBasic/truncatable-primes-2.purebasic

@@ -0,0 +1,30 @@
+maxprime = 1000000
+
+def primes(n):
+    multiples = set()
+    prime = []
+    for i in range(2, n+1):
+        if i not in multiples:
+            prime.append(i)
+            multiples.update(set(range(i*i, n+1, i)))
+    return prime
+
+def truncatableprime(n):
+    'Return a longest left and right truncatable primes below n'
+    primelist = [str(x) for x in primes(n)[::-1]]
+    primeset = set(primelist)
+    for n in primelist:
+        # n = 'abc'; [n[i:] for i in range(len(n))] -> ['abc', 'bc', 'c']
+        alltruncs = set(n[i:] for i in range(len(n)))
+        if alltruncs.issubset(primeset):
+            truncateleft = int(n)
+            break
+    for n in primelist:
+        # n = 'abc'; [n[:i+1] for i in range(len(n))] -> ['a', 'ab', 'abc']
+        alltruncs = set([n[:i+1] for i in range(len(n))])
+        if alltruncs.issubset(primeset):
+            truncateright = int(n)
+            break
+    return truncateleft, truncateright
+
+print(truncatableprime(maxprime))