Move Project Euler under puzzles.

puzzles/project_euler/p003_LargestPrimeFactor.cpp

@@ -0,0 +1,41 @@
+/* Check cf5-opt.vim defs.
+VIM: let g:lcppflags="-std=c++11 -O2 -pthread"
+VIM: let g:wcppflags="/O2 /EHsc /DWIN32"
+*/
+#include <iostream>
+
+/*
+Largest prime factor
+Problem 3
+The prime factors of 13195 are 5, 7, 13 and 29.
+
+What is the largest prime factor of the number 600851475143 ?
+
+Solution:
+6857
+*/
+
+long long max_factor( long long n )
+{
+	long long h = (long long)sqrt(double(n));
+	for ( long long i = 2; i <= h; )
+		if ( n%i )
+			++i;
+		else
+		{
+			n/=i;
+			h = (long long)sqrt(double(n));
+			//std::cout << "prime " << i << " " << n << std::endl;
+		}
+	//std::cout << "prime " << n << " 1" << std::endl;
+	return n;
+}
+
+int main ( void )
+{
+	const long long n = 600851475143;
+	std::cout << max_factor( n ) << std::endl;
+
+	return 0;
+}
+