Wikipedia
The McNuggets version of the coin problem was introduced by Henri Picciotto,
who included it in his algebra textbook co-authored with Anita Wah. Picciotto
thought of the application in the 1980s while dining with his son at
McDonald's, working the problem out on a napkin. A McNugget number is
the total number of McDonald's Chicken McNuggets in any number of boxes.
In the United Kingdom, the original boxes (prior to the introduction of
the Happy Meal-sized nugget boxes) were of 6, 9, and 20 nuggets.

Task

Calculate (from 0 up to a limit of 100) the largest non-McNuggets
number (a number n which cannot be expressed with 6x + 9y + 20z = n
where x, y and z are natural numbers).




include "cowgol.coh";
const LIMIT := 100;
 
var flags: uint8[LIMIT+1];
MemZero(&flags[0], @bytesof flags);
 
var a: @indexof flags;
var b: @indexof flags;
var c: @indexof flags;
 
a := 0;
while a <= LIMIT loop
    b := a;
    while b <= LIMIT loop
        c := b;
        while c <= LIMIT loop
            flags[c] := 1;
            c := c + 20;
        end loop;
        b := b + 9;
    end loop;
    a := a + 6;
end loop;
 
a := LIMIT;
loop
    if flags[a] == 0 then
        print("Maximum non-McNuggets number: ");
        print_i32(a as uint32);
        print_nl();
        break;
    end if;
    a := a - 1;
end loop;