Java 295 Cards

What is the result of evaluating the following postfix expression: 4 8 + 2 *

24

What is the @Test annotation?

@Test tells JUnit that the public void method to which it is attached can be run as a test case.

What's a Stack?

A classic collection used to help solve many types of problems A stack is a linear collection whose elements are added in a last in, first out (LIFO) manner That is, the last element to be put on a stack is the first one to be removed.

What is indirect recursion?

A method that invokes another method, which invokes another. Until the original method is invoked again.

What is a Unit Test case?

A part of code that ensures that another part of code works as expected.

Suppose a stack contains the values "Able", "Baker", "Charlie", "Delta" from top to bottom. What value is returned from 3 successive peek operations?

Abel

Tail recursion

All calculations happen first, then the reclusive call is the last thing that happens.

Whats a Collection?

An object that holds and organizes other objectsTheres linear and non-linear

Create a list and add 2, 3, and 4

ArrayList<Integer> list=new ArrayList<Integer>();list.add(2); list.add(3); list.add(4);

Size

Determines the number of elements

What exception is thrown if the pop method is called on an empty stack?

EmptyCollectionException

Recursions vs. Interation

Every tail recursive solution has a corresponding iterative solution.

Can all problems be solved with recursion methods? True or False

False

What is JUnit?

JUnit is a testing framework for Java.

Post fix expression

Just look at the operands on the right.(3 4 - (2 + 5)) 4 / 2 = 103 4 2 5 + - 4 2 / = 10

Pop

Removes an element from the top

What is a base case in recursion??

The code required to give the solution to the smallest subproblem.

How is a problem usually reduced with a recursive function?

The value of an argument is reduced.

What is infinite Recursion

When a recursive definition doesn't have a base case or the recursive case doesn't move towards a base case there is no way to terminate the recursive path. This will cause a stack overflow.

What is a recursive algorithm?

an algorithm that breaks the problem into smaller subproblems and applies the algorithm itself to solve the smaller subproblems

It is only possible to implement a stack using an array-based structure.

false

Create a for loop that will display Item1, Item2, Item3, Item4, Item5

for(int i=0; i<list.size(); i++)System.out.println(list.get(i));

Declare and instantiate an Array List (type String)

import.java.util.ArraList;ArrayList<String> list=new ArrayList<String>();

Given a string, compute recursively a new string where all the lowercase 'x' chars have been moved to the end of the string. endX("xxre") → "rexx"endX("xxhixx") → "hixxxx"endX("xhixhix") → "hihixxx"

public String endX(String str) { if (str.isEmpty()) { return ""; } if (str.charAt(0) == 'x') { return endX(str.substring(1)) + "x"; } return str.charAt(0) + endX(str.substring(1)); }

Given an array of ints, compute recursively if the array contains a 6. We'll use the convention of considering only the part of the array that begins at the given index. In this way, a recursive call can pass index+1 to move down the array. The initial call will pass in index as 0. array6([1, 6, 4], 0) → truearray6([1, 4], 0) → falsearray6([6], 0) → true

public boolean array6(int[] nums, int index) { if (index >= nums.length) { return false; } if (nums[index] == 6) { return true; } return array6(nums, index + 1); }

Given a non-negative int n, compute recursively (no loops) the count of the occurrences of 8 as a digit, except that an 8 with another 8 immediately to its left counts double, so 8818 yields 4. Note that mod (%) by 10 yields the rightmost digit (126 % 10 is 6), while divide (/) by 10 removes the rightmost digit (126 / 10 is 12). count8(8) → 1count8(818) → 2count8(8818) → 4

public int count8(int n) { if (n == 0) { return 0; } if (n % 10 == 8) { if ((n / 10) % 10 == 8) { return 2 + count8(n / 10); } return 1 + count8(n / 10); } return count8(n / 10); }

Write out a recursive method following the prompt We have bunnies standing in a line, numbered 1, 2, ... The odd bunnies (1, 3, ..) have the normal 2 ears. The even bunnies (2, 4, ..) we'll say have 3 ears, because they each have a raised foot. Recursively return the number of "ears" in the bunny line 1, 2, ... n (without loops or multiplication). bunnyEars2(0) → 0bunnyEars2(1) → 2bunnyEars2(2) → 5

public static int bunnyEars2(int n) { if (n == 0) { return 0; } else if (n % 2 == 0) { return 3 + bunnyEars2(n - 1); } else { return 2 + bunnyEars2(n - 1); } }

Which of the following methods inserts an element into a stack data structure?

push

Which of the following stack methods does not generate an exception?

push

Suppose a stack did not have an isEmpty() method. Which of the following conditions would provide an equivalent test?

size ()==0

A stack is a LIFO structure

true