CS100J Fall 2006 Sample answers for prelim 3
1. x= 0;
for (int k= b.length; 0 != k; k= k – 1) {
if (b[k–1] == b[k+x–1])
x= x + 1;
}
}
2. /** = index of the seller in deal[h..k] with best deal.
Precondition: d[h..k] is not empty*/
private int findBest(int h, int k) {
int best= h;
// inv: d[best] is the best deal in d[h..j-1]
for (int j= h+1; j <= k; j= j+1) {
Deal n= deal.get(j);
Deal b= deal.get(h);
if (n.getPrice() < b.getPrice() ||
(n.getPrice() == b.getPrice() &&
n.getCondition() > b.getCondition())) {
best= j;
}
}
return best;
}
/** Sort the deals for the textbook by price … */
public void sortSellers() {
// inv: deal[0..k-1] is sorted, and
// elements in deal[0..k-1] are better than
// elements in d[k..deal.size()-1]
for (int k= 0; k != deal.size(); k= k+1) {
int j= findBest(k,deal.size()-1);
Deal temp= deal.get(j);
deal.set(j, deal.get(k));
deal.set(k, temp);
}
}
3.
(a) int[][] b= new int[][] { {1, 3, 6, 10}, {2, 5, 9, 13},
{4, 8, 12, 15}, {7, 11, 14, 16} };
(b)
(c) c[2].length
4. (a)
4b.
4c. 9 buttons.
5. /** Constructor: an instance with value k.
Precondition: k > 0 */
public Positive (int k) {
this.k= k;
}
/** Constructor: an instance with rational
number num / denom.
Precondition: denom != 0 */
public Rational(int num, int denom) {
super(Math.abs(denom));
if (denom < 0)
this.num= – num;
else this.num= num
reduce();
}
/** Set the value of the denominator to n.
Precondition: n > 0 */
public void setPositive(int n){
super.setPositive(n);
reduce();
}
c
a1
null
a2
a3
a1
4
5
6
a2
1
2
a3
box
GUI(int)
addButtons(int, int)
null
a1
JFrame
GUI
n cp
2
a1
GUI: 1
null