Data commit

Task/Truncatable-primes/Python/truncatable-primes.py

@@ -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))