Computer Science 15-100, Fall 2009
Class Notes: Problem-Solving Practice
Note: You may not use Java concepts we have not yet covered, including loops (do/while/for), conditionals ("if" statements or tertiary operators (?:)), arrays, or methods from any classes in java.util.* to solve these problems. While they may be helpful, every problem here is solvable without them.
class MyCode {
// This method (that does not use "if" statements or the conditional operator
// ?:), takes an integer score for a grade and returns a char representing
// the letter grade for that score, where scores of 90 or higher receive an A,
// 80-89 receive a B, 70-79 receive a C, 60-69 receive a D, and below 60
// receive an E.
public static char letterGrade(int score) {
return 'Z';
}
public static void testLetterGrade() {
System.out.print("Testing letterGrade... ");
assert(letterGrade(110) == 'A');
assert(letterGrade(100) == 'A');
assert(letterGrade(90) == 'A');
assert(letterGrade(89) == 'B');
assert(letterGrade(80) == 'B');
assert(letterGrade(79) == 'C');
assert(letterGrade(70) == 'C');
assert(letterGrade(69) == 'D');
assert(letterGrade(60) == 'D');
assert(letterGrade(59) == 'E');
assert(letterGrade(49) == 'E');
assert(letterGrade( 0) == 'E');
System.out.println("Passed all tests!");
}
public static void main(String[] args) {
testLetterGrade();
}
}
class MyCode {
// This method (that does not use "if" statements or the conditional operator
// ?:), takes one parameter, the number of minutes past midnight (which you
// may assume is non-negative) and returns a String with the current time in
// the usual HH:MM format, including leading zeroes when necessary for the
// minutes but not the hours (so you would print out "four minutes past
// 9 o’clock" as 9:04. You should not include "am" or "pm", but you must
// handle arbitrarily large values for the minutesPastMidnight parameter.
public static String timeString(int minutesPastMidnight) {
return "42";
}
public static void testTimeString() {
System.out.print("Testing timeString... ");
assert(timeString(3*60+5).equals("3:05"));
assert(timeString(3*60+59).equals("3:59"));
assert(timeString(11*60).equals("11:00"));
assert(timeString(11*60+59).equals("11:59"));
assert(timeString(0).equals("12:00"));
assert(timeString(1).equals("12:01"));
assert(timeString(59).equals("12:59"));
assert(timeString(60).equals("1:00"));
assert(timeString(59).equals("12:59"));
assert(timeString(12*60).equals("12:00"));
assert(timeString(100*12*60+8*60+3).equals("8:03"));
System.out.println("Passed all tests!");
}
public static void main(String[] args) {
testTimeString();
}
}
class MyCode {
// This method takes a date represented by three integers,
// the month (1-12), the day (1-31), and the year, and returns an
// integer representing the day-of-week for that date, where
// Sunday is 1, Monday is 2, and so on, and Saturday is 7.
// While there are several ways to do this, you must use
// this formula (from the most-excellent web site mathforum.org):
// N = d + 2m + [3(m+1)/5] + y + [y/4] - [y/100] + [y/400] + 2
// Then the remainder when you divide N by 7 is the day-of-week,
// where Saturday is 0 and Friday is 6. Note that these values for
// the days are not quite the same as those returned by this method.
// Here is mathforum's description of the formula:
// "d is the number or the day of the month, m is the number
// of the month, and y is the year. The brackets around the
// divisions mean to drop the remainder and just use the
// integer part that you get.
// Also, a VERY IMPORTANT RULE is the number to use for the
// months for January and February. The numbers of these months
// are 13 and 14 of the PREVIOUS YEAR. This means that to find
// the day of the week of New Year's Day [of 1998], 1/1/98,
// you must use the date 13/1/97."
// Note: you must make the adjustment to the month and year when
// appropriate. So, for example, the date of New Year's Day for
// 1998 would be obtained in the natural way: dayOfWeek(1, 1, 1998).
// You may ignore the cases where the month, day, or year are out of bounds.
public static int dayOfWeek(int month, int day, int year) {
return 42;
}
public static void testDayOfWeek() {
System.out.print("Testing dayOfWeek... ");
// On 2/5/2006, the Steelers won Super Bowl XL on a Sunday!
assert(dayOfWeek(2, 5, 2006) == 1);
// On 6/15/1215, the Magna Carta was signed on a Monday!
assert(dayOfWeek(6, 15, 1215) == 2);
// On 3/11/1952, the author Douglas Adams was born on a Tuesday!
assert(dayOfWeek(3, 11, 1952) == 3);
// on 4/12/1961, Yuri Gagarin became the first man in space, on a Wednesday!
assert(dayOfWeek(4, 12, 1961) == 4);
// On 7/4/1776, the Declaration of Independence was signed on a Thursday!
assert(dayOfWeek(7, 4, 1776) == 5);
// on 1/2/1920, Isaac Asimov was born on a Friday!
assert(dayOfWeek(1, 2, 1920) == 6);
// on 10/11/1975, Saturday Night Live debuted on a Saturday (of course)!
assert(dayOfWeek(10, 11, 1975) == 7);
System.out.println("Passed all tests!");
}
public static void main(String[] args) {
testDayOfWeek();
}
}
class MyCode {
// This method takes a street number (which you may assume is positive),
// and returns the street number of the nearest bus stop, where buses
// stop on streets that are multiples of 8 (8th, 16th, 24th, etc).
// So it behaves as such:
// nearestBusStop(11) returns 8
// nearestBusStop(13) returns 16
// But what about 12th street? It is equally far from 8th and 16th
// streets, but riders generally head towards town (0th street), and
// so they prefer the lower bus stop. Hence:
// nearestBusStop(12) returns 8
// You can assume there is a bus stop on 0th street, and again you
// can ignore the case where the street is negative).
// Remember: do not use conditionals, loops, arrays, etc.
// This can be done (in one line of code!) using only what we
// have covered Week #1's notes (in fact, using just addition,
// division and multiplication of integers).
public static int nearestBusStop(int street) {
return 42;
}
public static void testNearestBusStop() {
System.out.print("Testing nearestBusStop... ");
assert(nearestBusStop(0) == 0);
assert(nearestBusStop(4) == 0);
assert(nearestBusStop(5) == 8);
assert(nearestBusStop(8) == 8);
assert(nearestBusStop(11) == 8);
assert(nearestBusStop(12) == 8);
assert(nearestBusStop(13) == 16);
System.out.println("Passed all tests!");
}
public static void main(String[] args) {
testNearestBusStop();
}
}Carpe diem!