Solution to problem 37

src/Python/Problem037.py

@@ -9,10 +9,15 @@ Solution for problem 37 of Project Euler
 https://projecteuler.net/problem=37
 """
 
-from itertools import product
-from utils import timeit, is_prime
+from utils import timeit, list_primes, is_prime
 
+def is_truncatable_prime(number):
+    num_str = str(number)
+    for i in range(1, len(num_str)):
+        if not is_prime(int(num_str[i:])) or not is_prime(int(num_str[:-i])):
+            return False
 
+    return True
 
 @timeit("Problem 37")
 def compute():
@@ -27,28 +32,12 @@ def compute():
 
     NOTE: 2, 3, 5, and 7 are not considered to be truncatable primes.
     """
-
-    primes, ans = [], 0
-    for i in range(2,7):
-        candidates = product([1,2,3,5,7,9], repeat=i)
-        for t in candidates:
-            primes.append(''.join([str(d) for d in t]))
-
-    for p in primes:
-        trunc = True
-        if not is_prime(int(p)):
-            trunc = False
-            continue
-        for i in range(1, len(p)):
-            if not is_prime(int(p[i:])):
-                trunc = False
-                break
-            if not is_prime(int(p[:i])):
-                trunc = False
-                break
-        if trunc:
-            ans += int(p)
-    
+    ans = 0
+    primes = list_primes(1_000_000)
+    # Statement of the problem says this
+    for number in primes[4:]:
+        if is_truncatable_prime(number):
+            ans += number
     return ans