task1
Implement the function that checks whether a string is a valid identifier. A valid identifier is a non-empty string that starts with a letter or underscore and consists of only letters, digits and underscores.
task2
Change the 'sum' function so that it was declared as an extension to List
task3
Mastermind is a board game for two players. The first player invents a code and the second player tries to guess this code. A code is made up 4 coloured pins and their position. There are 6 colours to choose from and the same colour can be repeated multiple times.
task4
Add and implement an extension function 'isEmptyOrNull()' on the type String?. It should return true, if the string is null or empty.
task5
Declare the s variable to make the first line print null and the second one throw an exception
task6
Functions 'all', 'none' and 'any' are interchangeable, you can use one or the other to implement the same functionality. Implement the functions 'allNonZero' and 'containsZero' using all three predicates in turn. 'allNonZero' checks that all the elements in the list are non-zero; 'containsZero' checks that the list contains zero element. Add the negation before the whole call (right before 'any', 'all' or 'none') when necessary, not only inside the predicate.
task7
Mastermind in a functional style
task8
A string is nice if at least two of the following conditions are satisfied:
- It doesn't contain substrings bu, ba or be;
- It contains at least three vowels (vowels are a, e, i, o and u);
- It contains a double letter (at least two similar letters following one another), like b in "abba". Check whether a given string is nice.
task9
Taxi Park
The TaxiPark class stores information about registered drivers, passengers, and their trips. Your task is to implement six functions which collect different statistics about the data.
SubTask 1
fun TaxiPark.findFakeDrivers(): Collection Find all the drivers who didn't perform any trips.
SubTask 2
fun TaxiPark.findFaithfulPassengers(minTrips: Int): List Find all the clients who completed at least the given number of trips.
SubTask 3
fun TaxiPark.findFrequentPassengers(driver: Driver): List Find all the passengers who were driven by a certain driver more than once.
SubTask 4
fun TaxiPark.findSmartPassengers(): Collection If we consider "smart", a passenger who had a discount for the majority of the trips they made or took part in (including the trips with more than one passenger), find all the "smart" passengers. A "smart" passenger should have strictly more trips with discount than trips without discount, the equal amounts of trips with and without discount isn't enough.
Note that the discount can't be 0.0, it's always non-zero if it's recorded.
SubTask 5
fun TaxiPark.findTheMostFrequentTripDurationPeriod(): IntRange? Find the most frequent trip duration period among minute periods 0..9, 10..19, 20..29, and so on. Return any suitable period if many are the most frequent, return null if there're no trips.
SubTask 6
fun TaxiPark.checkParetoPrinciple(): Boolean Check whether no more than 20% of the drivers contribute 80% of the income. The function should return true if the top 20% drivers (meaning the top 20% best performers) represent 80% or more of all trips total income, or false if not. The drivers that have no trips should be considered as contributing zero income. If the taxi park contains no trips, the result should be false.
For example, if there're 39 drivers in the taxi park, we need to check that no more than 20% of the most successful ones, which is seven drivers (39 * 0.2 = 7.8), contribute at least 80% of the total income. Note that eight drivers out of 39 is 20.51% which is more than 20%, so we check the income of seven the most successful drivers.
To find the total income sum up all the trip costs. Note that the discount is already applied while calculating the cost.
task10
Implement the property 'foo' so that it produced a different value on each access. Note that you can modify the code outside the 'foo' getter (e.g. add additional imports or properties).
task11
Without modifying the class 'A' complete the code in 'main' so that an exception UninitializedPropertyAccessException was thrown. Then fix the newly added code in 'main' so that no exception was thrown.
task14
Rational Numbers
Your task is to implement a class Rational representing rational numbers. A rational number is a number expressed as a ratio n/d , where n (numerator) and d (denominator) are integer numbers, except that d cannot be zero. If the denominator is zero, you can throw an exception on creating a new instance of the class, e.g. IllegalArgumentException.
Examples of rational numbers are 1/2, 2/3, 117/1098, and 2/1 (which can alternatively be written simply as 2). Rational numbers are represented exactly, without rounding or approximation, which gives them the advantage compared to floating-point numbers.
Your task it to model the behavior of rational numbers, including allowing them to be added, subtracted, multiplied, divided and compared. All arithmetic and comparison operations must be available for rationals: +, -, *, /, ==, <, >= etc. Check whether a number belongs to a range should also be possible: 1/2 in 1/3..2/3 should return true.
The Rational class should contain a numerator and denominator which might be unlimited numbers, so use java.math.BigInteger class for storing them.
The rational numbers must be compared to their "normalized" forms: for example, 1/2 should be equal to 2/4, or 117/1098 to 13/122. The string representation of a rational must be also given in the normalized form. Note that the denominator 1 must be omitted, so 2/1 must be printed as "2". The denominator must be always positive in the normalized form. If the negative rational is normalized, then only the numerator can be negative, e.g. the normalized form of 1/-2 should be -1/2.
Note that you can use BigInteger.gcd to find the greatest common divisor used in the normalized form calculation.
You need to support two ways to create rationals. The first one is to convert a string representation to a rational directly, like in "1/2".toRational(). Converting an integer number should also be possible, and 1 should be used as denominator by default: "23".toRational() is the same as "23/1".toRational().
The alternative way to create a rational is to use divBy infix function like in 1 divBy 2. The receiver and the argument might be of types Int, Long, or BigInteger.