AP Computer Science Java Programming - Algorithms and Arrays

hansenator (57)in #tutorials • 7 years ago

Know this Steemers, when learning to read algorithms you need to read line by line, like a book, very slowly. If you do not it will be way harder than it has to be! Note: due to html/steemit some of the code is spaced because otherwise it will not show up (the programs will not run by if copy/pasted). Enjoy today's lesson!

Arrays

• An array is a “list” of strings or numbers.
• Designated List< int> name = new ArrayList< int>(); // Replace int with String, double, etc. (no spaces in < int >)
• Ex. – Say we had an array called names = [“John”, “Billy”, “Tom”, “Jerry”]. What is names[1]? Billy (because we count 0, 1, 2...)

AP Sample Problems

Example 1

Consider the following partial code:

for (int k = 0; k < 20; k = k + 2) { // k += 2 also works
if (k % 3 == 1) {
System.out.print(k + “ “);
}
}

What does it print?

Remember the % operator gives you the remainder, so all multiples of two, with remainder 1 when divided by 3, is what the program prints... Up to less than 20. (k + “ “) adds a space between each number.
Answer: 4 10 16

Example 2

Consider the partial program:

List< String> animals = new ArrayList< String>;
animals.add(“dog”);
animals.add(“cat”);
animals.add(“snake”);
animals.set(2, “lizard”);
animals.set(1, “fish”);
animals.remove(2);
System.out.println(animals);

The real thing to remember here is that element 0 is the first element, so the last element is the size of the array minus 1.
Answer: ["dog", "fish"]

Example 3

Consider the following method:

public static void main(String[] args) {
for (int k = 0; k < nums.size(); k++) {
if (nums.get(k).intValue() == 0) {
nums.remove(k);
}
}
}

Assume that a List< integer> values initially contains the following
values:
[0, 0, 4, 2, 5, 0, 3, 0]
What will the main method print when it executes?

[0, 4, 2, 5, 3] because when the loop runs it deletes the first zero, skips the second zero because it moves on the the second element, but gets rid of the rest of the zeros.