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Problem #1:
2 points each, 1 point for correct value of wrong type (missing parens, no .0)
Problem #2:
1 point for each of the 12 values
-1 if any error in surrounding text (dittos not allowed)
-4 if two columns transposed
-8 if you need to transpose twice
Problem #3:
each is 3 points, -1 for a single number wrong or for a single transpose
-2 overall if columns transposed
-2 if formatting error (e.g., commas between numbers)
-1 if individual pair is reversed
-0 if output is quoted
-0 if underscore for space
Problem #4:
column 1 is 1 point, column 2 is 2 points
-2 overall if columns transposed
-2 if formatting error (e.g., commas between numbers)
-1 if individual pair is reversed
-0 if output is quoted
-0 if underscore for space
Problem #5:
1 point per blank
Problem #6
Solutions:
public static int numUnique(int x, int y, int z) {
if (x == y && y == z) {
return 1;
} else if (x != y && x != z && y != z) {
return 3;
} else {
return 2;
}
}
public static int numUnique2(int x, int y, int z) {
if (x == y) {
if (y == z) {
return 1;
} else {
return 2;
}
} else { // x != y
if (y == z) {
return 2;
} else if (x == z) {
return 2;
} else {
return 3;
}
}
}
public static int numUnique3(int x, int y, int z) {
int count = 0;
if (x != y) {
count++;
}
if (y != z) {
count++;
}
if (x != z) {
count++;
}
if (count == 0) {
count = 1;
}
return count;
}
2 header (-1 per error)
13 correctly distinguishes cases (requires idea)
4 returns 1 when appropriate: (5, 5, 5)
2 reasonable attempt (trying to test for this case, return 1)
2 correct (always returns 1 for this case based on tests)
4 returns 3 when appropriate: (4, 5, 6)
2 reasonable attempt (trying to test for this case, return 3)
2 correct (always returns 3 for this case based on tests)
5 returns 2 when appropriate: (4, 5, 5); (5, 4, 5); (5, 5, 4)
2 reasonable attempt (trying to test for this case, return 2)
3 correct (always returns 2 for this case based on tests)
Notes:
-3 for single global change that increases their score. For example: printing
instead of returning (then they can have a void method).
Problem #7
Solution:
public static void printNumbers(Random r) {
int n = r.nextInt(50) + 1;
System.out.print("[" + n);
while (n % 10 != 5) {
n = r.nextInt(50) + 1;
System.out.print(", " + n);
}
System.out.println("]");
}
public static void printNumbers2(Random r) {
System.out.print("[");
int n = r.nextInt(50) + 1;
while (n % 10 != 5) {
System.out.print(n + ", ");
n = r.nextInt(50) + 1;
}
System.out.println(n + "]");
}
1 correct header (non-void return okay if they return something of that type)
2 expression for generating random numbers from 1 to 50: r.nextInt(50) + 1
1 attempt (uses Random, either the 50 is right or the +1 is right)
1 correct (both are correct and they do it right everywhere)
4 loop until they get a number ending in 5 (ignoring fencepost)
1 a loop with some attempt to test for n ending in 5
2 correct loop test
2 loop generates a new value for n each time through the loop and they
aren't doing something silly like printing one random and testing another
3 printing (ignoring fencepost)
1 prints left and right brackets (println ok)
1 prints a comma either before or after each number (println ok)
1 overall print correctness ignoring fencepost: print("[") before loop,
print(n && ",") in loop, print or println("]") after loop
4 solved fencepost problem
1 attempt to solve this problem
3 correct (-1 if some minor error like reversing order of number/comma)
Problem #8
Solutions:
public static int numWords(String s) {
int count = 0;
boolean inWord = false;
for (int i = 0; i < s.length(); i++)
if (s.charAt(i) == ' ')
inWord = false;
else if (!inWord) {
count++;
inWord = true;
}
return count;
}
public static int numWords(String s) {
int count = 0;
for (int i = 1; i < s.length(); i++)
if (s.charAt(i - 1) == ' ' && s.charAt(i) != ' ')
count++;
if (s.length() > 0 && s.charAt(0) != ' ')
count++;
return count;
}
public static int numWords(String s) {
int count = 0;
int i = 0;
while (i < s.length()) {
while (i < s.length() && s.charAt(i) == ' ')
i++;
if (i < s.length()) {
count++;
while (i < s.length() && s.charAt(i) != ' ')
i++;
}
}
return count;
}
Can get up to 3 points for any of the following good things:
1 correct header
1 for loop involving s.length
1 initializing a counter variable
1 returning a counter variable after a loop
1 s.charAt(i) or s.substring(i, i + 1)
1 testing whether charAt or substring is equal or not equal to a space (don't
worry about syntax if the intent is clear)
1 using s.indexOf(" ") or s.indexOf(' ')
1 comparing charAt(i) with charAt(i + 1) (or substring)
Pass into round 2 if it has some hope of working:
* testing adjacent characters for a space/nonspace combination (or using a
previous character or flag variable to do so)
* a nested loop approach that involves skipping past a word
* using s.indexOf(" ") to skip over a word
When in doubt, pass on to round 2.
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Stuart Reges
Last modified: Fri Sep 16 15:55:46 PDT 2011