Info 2 Finger Exercises

This is a small collection of programming finger exercises to get you back to programming java, and to get to know your new programming environment.

I’ve numbered them for easier referencing in the Q&A.

Basic Exercises

FE_1: Count 0s in an array

Write a method that takes an integer array as parameter and returns the number of 0 contained in it.

FE_2: Count occurrences of an character in a String

Write a method that takes a String s and a character c as parameters and returns the number of occurrences of c in s.

Recursion

FE_r_1: Factorial

The factorial function ! is defined as: n! = n x (n-1) x (n-2) x (n-3) x …. x 3 x 2 x 1. e.g. 5! = 5 x 4 x 3 x 2 x 1 = 120 0! is defined as 1.

The factorial can also be expressed with the recurrence relation n! = n * (n-1)! Which leads to a recursive implementation:

fac(n): if (n == 0) return 1 else return n * fac(n-1)

Implement and test this as a Java Programm.

Little Challenges

FE_x_1: Pairs that add up to 0

Write a method that takes an integer array as parameter finds pairs that add up to 0.

• just count the number of pairs and return it as an int
• return the pairs as an array of two-element arrays containing the pairs

FE_x_2: Palindrome

A palindrome is a string or sentence that reads the same backwards as forwards, e.g.

• rentner
• lagerregal
• racecar
• Do Geese See God?
• Dammit, I’m Mad!

Write a method that determines wether a String is a palindrome: a) iteratively (with a loop) b) recursively