Prelim 2 Solution Guide

Median =  79

1.(a) 10 points

20
10
XX

-3 if concatenation wrong -7 for things like

20
10
0
XIXI

(b) 10 points

String c1 = s.substring(0,1);
String c2 = s.substring(1,2);
B = c1.equals(c2);

5points for the substrings and 5 for the boolean assignment. -3 for equals(c1,c2). -1 if indices off by 1. -2 for using uninitialized variable.

2. Output:

y = 11                         3 points
x = 11  y = 10  z = 30         3 + 3 + 1 points
y = 2                          2 points
z = 4                          2 points
x = 1  y = 10   z = 4          2 + 2 + 2 points

3(a) 10 points

boolean twoOrThree = (n%2==0) || (n%3==0);
boolean fiveOrSeven = (n%5==0) || (n%7==0);
return twoOrthree && fiveOrSeven;

-5 if ands and ors mixed up, - 3 for syntax like "return nearlyPrime", -2 for == instead of ==, -3 if no return.

3(b) 10 points

int sum = 0; 
for(int k=1;k<=1000000;k++) 
{
 if(A.nearlyPrime(k)) 
    { sum=sum+k; }
 
} 
System.out.println(sum); 

-2 for no A., -2 if sum not initialized, -3 if print inside loop, -6 if no if, -3 if wrong sum update, -6 if the nearlyPrime method is not used.

4(a) 8 points

if (m>D.m)
   return true;
else if (D.m > m)
   return false;
else if (d > D.d)
   return true;
else
   return false;

Or this:
 return (m>D.m) || ((m==D.m) && (d>D.d));

-5 for (m>D.m) || (d>D.d). -3 if dont return a boolean, -2 if you solve the "earlier than" problem, -3 if you use mVal not m, or dVal instead of D.

4(b) 12 points

SimpleDate June15 = new SimpleDate(6,15);  // Represent June 15th            4 points for this. -1 if no new
SimpleDate D0 = SimpleDate.random();       // Represent the random date     4 points, -1 if include a new
if ( D0.isLaterThan(June15))              // 4 points for using isLaterThan correctly
   system.out.println("Yes");
else
   System.out.println("No");

-5 if youdo not use isLaterThan, -7 if you don't use parameters in the method call.

5.

g.setColor(Color.black);
g.fillOval(hc-r,vc-r,2*r,2*r);
g.setColor(Color.yellow);
int d;
for(int v=vc-r;v<=vc+r;v++)
{
  d = (int) math.sqrt(r*r - (v-vc)*(v-vc));
  if (q==1)
     g.drawLine(hc,v,hc+d,v);
  else if (q==2)
     g.drawLine(hc-d,hc+d,v);
  else if (q==3)
     g.drawLine(hc-d,v,hc,v);
}

-6 if the default does not draw a new moon, -5 if the d computation is wrong, -2 if drawLine is handed a type double value, -5 if missing hc in drawLine, -10 if some how try to draw the 1st and 3rd quarter with fillOval, -3 if drawOval instead of fillOval, -12 if just a skeletal solution