project_euler/problem_10

project_euler/problem_10/sol3.py

@@ -0,0 +1,64 @@
+"""
+https://projecteuler.net/problem=10
+
+Problem Statement:
+The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
+
+Find the sum of all the primes below two million.
+
+using Sieve_of_Eratosthenes : 
+
+The sieve of Eratosthenes is one of the most efficient ways to find all primes smaller than n when n is smaller than 10 million
+"""
+
+try:
+    raw_input  # Python 2
+except NameError:
+    raw_input = input  # Python 3
+
+try:
+    xrange  # Python 2
+except NameError:
+    xrange = range  # Python 3
+
+
+def prime_sum(n):
+    """Returns the sum of all the primes below n.
+
+
+        >>> prime_sum(2000000)
+        142913828922
+        >>> prime_sum(1000)
+        76127
+        >>> prime_sum(5000)
+        1548136
+        >>> prime_sum(10000)
+        5736396
+        >>> prime_sum(7)
+        10
+
+    """
+
+    list = [0 for i in xrange(n+1)]
+
+    list[0]=1
+    list[1]=1
+
+    for i in xrange(2,int(n**0.5)+1):
+        if list[i]==0:
+            for j in xrange(i * i, n+1, i):
+                    list[j]=1
+    s=0
+    for i in xrange(n):
+        if list[i] == 0:
+            s+=i
+    return(s)
+
+if __name__ == '__main__':
+
+    #import doctest
+    #doctest.testmod()
+
+    print(prime_sum(int(raw_input())))
+
+