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Key to CSE143X Midterm, Winter 2025 handout #14
1. Method Call Value Returned
-----------------------------------------------
mystery(42, 0) 0
mystery(5, 25) 1
mystery(752, 792) 2
mystery(3092, 5028) 1
mystery(61903, 1930) 2
2. One possible solution appears below.
public String groupChars(String s) {
if (s.length() == 0) {
return "*";
} else if (s.length() < 3) {
return "[" + s + "]";
} else {
int last = s.length() - 1;
return "(" + s.charAt(0) + groupChars(s.substring(1, last)) +
s.charAt(last) + ")";
}
}
3. Statement Output
------------------------------------------------------------
var1.method1(); compiler error
var2.method1(); Doll 1
var1.method2(); Truck 2/Ball 2/Truck 3
var2.method2(); Doll 2
var3.method2(); Truck 2/Ball 2/Block 3
var4.method2(); compiler error
var5.method2(); Truck 2/Ball 2/Block 3
var1.method3(); Truck 3
var2.method3(); Ball 3
var3.method3(); Block 3
var4.method3(); compiler error
var5.method3(); Block 3
((Doll)var3).method1(); runtime error
((Block)var5).method1(); Block 1
((Truck)var3).method1(); compiler error
((Truck)var3).method3(); Block 3
((Block)var6).method3(); runtime error
((Ball)var4).method2(); Ball 2
((Truck)var4).method3(); runtime error
((Doll)var6).method3(); Ball 3
4. before after code
-----------------------+-----------------------+-------------------------------
p->[1]->[2] | p->[1] | q.next = p.next;
| | p.next = null;
q->[3] | q->[3]->[2] |
-----------------------+-----------------------+-------------------------------
p | p->[1] | p = q;
| | q = q.next;
q->[1]->[2]->[3] | q->[2]->[3] | p.next = null;
-----------------------+-----------------------+-------------------------------
p->[1]->[2]->[3] | p->[3]->[1] | p.next.next.next = p;
| | p = p.next.next;
q->[4] | q->[2]->[4] | p.next.next.next = q;
| | q = p.next.next;
| | p.next.next = null;
-----------------------+-----------------------+-------------------------------
p->[1] | p->[5]->[1]->[3] | p.next = q.next;
| | q.next.next.next.next = p;
q->[2]->[3]->[4]->[5] | q->[4]->[2] | p = q.next.next.next;
| | q.next.next.next = q;
| | q = q.next.next;
| | q.next.next = null;
| | p.next.next.next = null;
-----------------------+-----------------------+-------------------------------
5. One possible solution appears below.
public ArrayIntList fromCounts() {
ArrayIntList result = new ArrayIntList();
int size2 = 0;
for (int i = 0; i < size; i += 2) {
for (int j = 0; j < elementData[i]; j++) {
result.elementData[size2] = elementData[i + 1];
size2++;
}
}
result.size = size2;
return result;
}
6. One possible solution appears below.
public static void mirrorCollapse(Stack<Integer> s) {
Queue<Integer> q = new LinkedList<>();
while (!s.isEmpty()) {
q.add(s.pop());
}
int oldSize = q.size();
for (int i = 0; i < oldSize / 2; i++) {
s.push(q.remove());
}
if (oldSize % 2 == 1) {
q.add(q.remove());
}
while (!s.isEmpty()) {
q.add(q.remove() + s.pop());
}
while (!q.isEmpty()) {
s.push(q.remove());
}
}
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