Description
Warm-up Question 1 (0 points)
Create a file called Counting.java, and in this file, declare a class called Counting. This program takes
as input from the user a positive integer and counts up until that number. eg:
run Counting 10
I am c o u n ti n g u n t i l 1 0: 1 2 3 4 5 6 7 8 9 10
Warm-up Question 2 (0 points)
For this question you have to generalize the last question. The user will give you the number they want
the computer to count up to and the step size by which it will do so.
run Counting 25 3
I am c o u n ti n g t o 25 with a s t e p s i z e o f 3 :
1 4 7 10 13 16 19 21 24
1
Warm-up Question 3 (0 points)
Write a method reverseString which takes as input a String and returns the string in reverse order.
For example if the input String is “Comp 202 is awesome” the result should be “emosewa si 202 pmoC”
Hint: Use a new String called reverse and initially store into it the empty String. Then read the
input String in reverse by using the method .charAt(int i) to get a specific element.
Warm-up Question 4 (0 points)
A prime number is a positive number whose only even divisors are 1 and itself. Write a method isPrime
that takes as input an integer n and returns a boolean representing whether n is prime or not. Make
sure to handled cases where the integer is negative. (Your method should return false in these cases.)
Warm-up Question 5 (0 points)
Write a method firstPrimeNumbers which takes as input an int n and returns an int[] . The int[]
should contain the first n prime numbers.
Warm-up Question 6 (0 points)
This program prints the outline of a square made up of # signs. It should take as input the length of the
sides in number of #s. Using two loops, you should be able to draw the outline of a square as follows.
##########
# #
# #
# #
# #
# #
# #
# #
# #
##########
N.B. It is normal that the square does not appear to be a perfect square on screen as the width and the
length of the characters are not equal.
Part 2
The questions in this part of the assignment will be graded.
Question 1: Drunken Sailor (30 points)
Consider a sailor who gets out of a bar completely drunk, in a city where all blocks are in perfect squares
with size 1 × 1. The drunken sailor walks from one corner of a block to the next. When in a corner, he
forgets where he came from, and where he was going. He takes a direction at random, either north, east,
south, or west, with an equal probability of 25%. Then in the following corner he again forgets where he
was going, but keeps on walking by following a random direction. You will write a program that takes
an integer input N, and simulates the motion of the drunken sailor for N steps. After each step, print
the location of the sailor. You can treat the starting point as (0, 0). Also, print the final distance from
the origin and the furthest point1 he has reached. Example:
>run D run kenS ail o r 10
( 0 , −1)
( 0 , 0 )
( 0 , 1 )
( 0 , 2 )
( −1, 2 )
( −2, 2 )
( −2, 1 )
( −1, 1 )
( −2, 1 )
1We use the Euclidean distance here. In particular, the distance between (x, y) and the origin is p
x2 + y
2. The furthest
point is the point with the largest Euclidean distance from the origin.
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Figure 1: An example of an 8-step walk by the sailor.
( −3, 1 )
Fi n al di s t a n c e = 3. 1 6 2 2 7 7 6 6 0 1 6 8 3 7 9 5
F u r t h e s t p oi n t = ( −3 ,1)
Question 2: Binary Converter (35 points)
You will write a program that converts binary numbers to decimal numbers, where the input binary
number is a String. This program will first verify whether the input only contains ‘0’s and ‘1’s.2
If
the user enters letters or other invalid inputs, the program prints “The input is not binary!”. When the
input is valid, the program will then convert the binary number to a decimal number.
Valid input – In order to check if the input is valid your program should check if it is only composed of
zeros and ones. More specifically, you should scan the input string using a for or while loop to make sure
it only contains ‘0’ or ‘1’ characters. As soon as you find a character that is not ‘0’ or ‘1’, the process
should stop. If the process reaches the end of the input string then we have a valid input. You may
ignore the case where the input string is empty, as well as any extra ‘0’s at the start of the string.
Converting – At this point we assume that the input string is valid. The binary conversion should
work as follows. For each digit in the binary number, if the digit is ‘1’ you should add the corresponding
decimal value ( 20
for the rightmost digit, 21
for the next digits to the left, 22
for the next one, and so
on) to a variable that will hold the final result to be printed. This must be accomplished by using a
loop.
Example:
> run C onve r si on 123456789
The i n p u t i s not bi n a r y !
>run C onve r si on 101010
The bi n a r y number 101010 i s 42 i n b a se 1 0.
Question 3: Arrays (35 points)
3a) Find the Missing Numbers
Write a method findMissingNum that takes two inputs: a positive integer n and an integer array which
contains numbers from 1 to n. Some integer numbers in this range are missing in the array, you need
to write a Java program to find those missing numbers in the array and print them out. If no number
is missing, print out “No number is missing!”.
Example:
2
IMPORTANT: You are allowed to use loops, the length(), charAt(int index) and equals(String other) methods of
Strings for this question.
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findMissingNum(6, array) while array = {2, 3, 5, 1, 2, 3} should print out 4, 6.
findMissingNum(5, array) while array = {1, 5, 1, 3, 4, 2} should print out “No number is missing!”.
findMissingNum(4, array) while array is empty should print out 1, 2, 3, 4.
3b) Find the Most Frequent Numbers
Implement a method findMostFrequent that again takes a positive integer n and an integer array which
contains numbers from 1 to n. Print out all the numbers that have the highest frequency.
Example:
findMissingNum(6, array) while array = {2, 3, 5, 1, 2, 3} should print out 2, 3.
findMissingNum(5, array) while array = {1, 5, 1, 3, 4, 2} should print out 1.
findMissingNum(4, array) while array is should print out “The array is empty!”.
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What To Submit
You have to submit one zip file that contains all your files to myCourses – Assignment 2. If you do not know
how to zip files, please enquire that information from any search engine or friends. Google might be your
best friend with this, and for a lot of different little problems as well.
DrunkenSailor.java – Java code
Conversion.java – Java code
arrays.java – Java code
Confession.txt (optional) In this file, you can tell the TA about any issues you ran into doing
this assignment. If you point out an error that you know occurs in your problem, it may lead
the TA to give you more partial credit. On the other hand, it also may lead the TA to notice
something that otherwise he or she would not.
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