added solution 4 for problem_20 (#1476)

project_euler/problem_20/sol4.py

@@ -0,0 +1,40 @@
+"""
+n! means n × (n − 1) × ... × 3 × 2 × 1
+
+For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,
+and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
+
+Find the sum of the digits in the number 100!
+"""
+
+
+def solution(n):
+    """Returns the sum of the digits in the number 100!
+    >>> solution(100)
+    648
+    >>> solution(50)
+    216
+    >>> solution(10)
+    27
+    >>> solution(5)
+    3
+    >>> solution(3)
+    6
+    >>> solution(2)
+    2
+    >>> solution(1)
+    1
+    """
+    fact = 1
+    result = 0
+    for i in range(1,n + 1):
+        fact *= i
+
+    for j in str(fact):
+        result += int(j)
+
+    return result
+
+
+if __name__ == "__main__":
+    print(solution(int(input("Enter the Number: ").strip())))