Add solution for problem 36.

README.md

@@ -1,6 +1,6 @@
 # [Project Euler](https://projecteuler.net) Solutions
 
-[![solved: 35 problems](https://img.shields.io/badge/solved-35_problems-f93.svg)](./src)
+[![solved: 36 problems](https://img.shields.io/badge/solved-36_problems-f93.svg)](./src)
 ![Python: 3.7](https://img.shields.io/badge/Python-3.7-3776ab.svg)
 [![Build Status](https://travis-ci.com/FranzDiebold/project-euler-solutions.svg?branch=master)](https://travis-ci.com/FranzDiebold/project-euler-solutions)
 [![license: MIT](https://img.shields.io/badge/license-MIT-brightgreen.svg)](./LICENSE.md)

src/common/palindromes.py

@@ -0,0 +1,14 @@
+"""
+Palindrome utility functions.
+"""
+
+from typing import Union
+
+
+def is_palindromic_number(number: Union[int, str]) -> bool:
+    """Check if a number is palindromic number."""
+    number_str = str(number)
+    for i in range(len(number_str) // 2):
+        if number_str[i] != number_str[-1 * (i + 1)]:
+            return False
+    return True

src/p004_largest_palindrome_product.py

@@ -11,14 +11,7 @@
 from typing import Iterator, Tuple
 from heapq import heappush, heappop
 
-
-def is_palindromic_number(num: int) -> bool:
-    """Check if a number is palindromic number."""
-    num_str = str(num)
-    for i in range(len(num_str) // 2):
-        if num_str[i] != num_str[-1 * (i + 1)]:
-            return False
-    return True
+from src.common.palindromes import is_palindromic_number
 
 
 def _get_lower_diagonal_tuples(tuple_sum: int, max_value: int) -> Iterator[Tuple[int, int]]:

src/p036_double_base_palindromes.py

@@ -0,0 +1,41 @@
+"""
+Problem 36: Double-base palindromes
+http://projecteuler.net/problem=36
+
+The decimal number, 585 = 1001001001 (binary), is palindromic in both bases.
+
+Find the sum of all numbers, less than one million, which are palindromic in base 10 and base 2.
+
+(Please note that the palindromic number, in either base, may not include leading zeros.)
+"""
+
+from typing import Iterable
+
+from src.common.palindromes import is_palindromic_number
+
+
+def _get_number_in_binary(number: int) -> str:
+    """Get the binary representation of a given decimal number `number` as string."""
+    binary_representation = ''
+    while number > 0:
+        binary_representation = str(number % 2) + binary_representation
+        number //= 2
+    return binary_representation
+
+
+def _get_double_base_palindromes(threshold: int) -> Iterable[int]:
+    """Get numbers, which are paldindromic in base 10 and base 2."""
+    for number in range(threshold):
+        if is_palindromic_number(number) and is_palindromic_number(_get_number_in_binary(number)):
+            yield number
+
+
+def main() -> None:
+    """Main function."""
+    threshold = int(1e6)
+    print(f'The sum of all numbers, less than {threshold:,}, which are palindromic ' \
+          f'in base 10 and base 2 is {sum(_get_double_base_palindromes(threshold)):,}.')
+
+
+if __name__ == '__main__':
+    main()