The Problem:

What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20

My Solution (in C++):

// Author: Will Clausen // // Date: Jan 7, 2013 // // This program will solve Problem 5 from Project Euler. // I had previously written a solution to this problem in // python, but it is not fast enough (primarily becuase I // did not think cleverly about the problem). #include <iostream> #include <cstddef> using namespace std; size_t gcd(size_t a, size_t b); size_t lcm(size_t a, size_t b); size_t problem5(size_t maxDivisor) { size_t LCM = 1; for (size_t i = 1; i <= maxDivisor; ++i) { LCM = lcm(LCM, i); } return LCM; } size_t gcd(size_t a, size_t b) { if (b == 0) return a; if (b <= a) return gcd(b, a%b); else return gcd(b, a); } size_t lcm(size_t a, size_t b) { return (a*b/gcd(a,b)); } // Output with maxDivisor 20: 232792560