Problem5-Project Euler

Smallest multiple

 

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?

考虑质因数分解，将1-20都分解，挑质因数的最高幂次相乘即可。

 #include"stdio.h"
 #include"math.h"

 #define N 20

 int prime[N+];

 int find_prime(int x)
 {
     int i,j,sum=;
     for(i=;i<=x;i++)
     {
         prime[i]=;
         for(j=;j<=int(sqrt(i));j++)
             if(i%j==)
                 prime[i]=;
         if(prime[i]!=&&i>=)
         {
             prime[i]=int(log(x)/log(i));
             sum *= int(pow(i,prime[i]));
         }
     }
     return(sum);
 }

 int main()        /*problem5-smallest multiple*/
 {
     printf("answer is %d\n",find_prime(N));
     return();
 }