Project Euler #5 in Java: stuck in the end of program

debugcn Published at Dev

Vaibhav Agarwal

I am trying to get the smallest positive number that is evenly divisible by all of the numbers from 1 to 20. But somehow I am stuck in the end of the program. My answer is coming 40 which is wrong. Here is my code:

public class Lessons {

    public static void main(String[] args) {
        int n;
        int s = 0;

        for (n = 21; n > 0; n++) 
        {
         for (int m = 1; m <= 20; m++) 
           {
                s = n % m;
            }
            if (s == 0) 
             {
                System.out.println(n);
                break;
            }

        }
    }
}

Any helps???

lc.

You're effectively only ever checking whether n%20 == 0. This loop:

for (int m = 1; m <= 20; m++) {
    s = n % m;
}

does run for m from 1 to 20, but you always overwrite s and never do anything with the value before resetting it the next time through the loop. You need to check the result of n % m for each iteration of the loop, perhaps like:

    for (n = 21; n > 0; n++) {
        bool divisibleByAll = true;

        for (int m = 1; m <= 20; m++) {
            s = n % m;

            if(s != 0) {
                divisibleByAll = false;
                break; //don't bother checking the rest
            }
        }

        if (divisibleByAll) {
            System.out.println(n);
            break;
        }

    }

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