Project Euler: http://projecteuler.net/

ProjectEuler/p005_SmallestMultiple.cpp

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+/* Check cf5-opt.vim defs.
+VIM: let g:lcppflags="-std=c++11 -O2 -pthread"
+VIM: let g:wcppflags="/O2 /EHsc /DWIN32"
+*/
+#include <iostream>
+#include <exception>
+
+/*
+Smallest multiple
+Problem 5
+
+2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.
+
+What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?
+
+Solution:
+232792560
+*/
+
+long long lacking_factor( long long n, long long m )
+{
+	long long h = (long long)sqrt(double(n));
+	long long l = 1;
+	for ( long long i = 2; i <= h; )
+		if ( n%i )
+			++i;
+		else
+		{
+			n/=i;
+			h = (long long)sqrt(double(n));
+			if ( m%i )
+				l*=i;
+			else
+				m/=i;
+		}
+			
+	if ( m%n )
+		l *= n;
+	return l;
+}
+
+
+int main ( void )
+{
+	long long m = 1;
+	for ( int i = 2; i <= 20; ++i )
+	{
+		m *= lacking_factor( i, m );
+		//std::cout << i << " " << m << std::endl;
+	}
+
+	std::cout << m << std::endl;
+
+	return 0;
+}
+