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lfa:2022:lab01-programming-intro [2022/10/07 15:36]
pdmatei 		lfa:2022:lab01-programming-intro [2022/10/14 13:13] (current)
mihai.udubasa add solutions
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 ===== 1. Scala introduction ===== ===== 1. Scala introduction =====
- 
  
 **Exercise 1.1.** Write a function ​ ''​startStop''​ which retrieves the elements of a list from within bounds. Use patterns in your implementation. Define an object ''​Main''​ as shown below. **Exercise 1.1.** Write a function ​ ''​startStop''​ which retrieves the elements of a list from within bounds. Use patterns in your implementation. Define an object ''​Main''​ as shown below.
-Any code within the object can be directly executed.+Any code within the object can be directly executed. ​(Hint: use a simply-recursive function)/
  
 <code scala> <code scala>
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 </​code> ​ </​code> ​
  
-**Exercise 1.2.**+**Exercise 1.2.** ​Write a function which determines the number of occurrences of each character in a string. (Hint: use a tail-recursive function) 
 +<code scala> 
 +def countChars (s:String): Map[Char,​Int] = { 
 +    def aux(l: List[Char], acc: Map[Char,​Int]):​ Map[Char,​Int] = ??? 
 +    ??? 
 +  } 
 +</​code>​ 
 + 
 +**Exercise 1.3** Write a function which takes a list of records first name, last name, CNP (encoded as tuples), and returns a list of the last names and ages of all females which are younger than the average of the entire list. E.g. ''​List( (“Mary”,​ “2030694123456”),​ (“Anne”,​“2121092123456”),​ (“Matei”,​ “5121202123456”),​ (“Maggie”,​ “2121078123456”) )''​ yields ''​List( (“Mary”,​28),​ (“Anne”,​30) )''​. Maggie was born in '78, whereas Mary, Anne and Matei were born in '94, '92 and 2002, respectively. (Hint: use combinations of **map** with **filter**) 
 + 
 +<code scala> 
 +val example = List(("​Mary", ​ "​2030694123456"​),​ ("​Anne", ​ "​2121092123456"​),​ ("​Matei",​ "​5121202123456"​),​ ("​Maggie",​ "​2121078123456"​)) 
 + 
 +def youngerThanAverage(l:​ List[(String,​String)]):​ List[(String,​Int)] = { 
 +    def getAge(s:​String):​Int = ???  
 +    // female gender = True 
 +    def getGender(s:​String):​Boolean = ??? 
 +    ??? 
 +  } 
 +</​code>​ 
 + 
 +**Exercise 1.4**  
 +A labelled graph is encoded as a String text where **each line** is an edge ''<​from>​ <​label>​ <​to>''​ 
 +Example: 
 +<​code>​ 
 +0 r 1 
 +0 r 2 
 +0 g 1 
 +1 g 2  
 +1 b 3 
 +1 r 4 
 +4 g 1 
 +3 b 2 
 +2 r 2 
 +2 g 3 
 +</​code>​ 
 + 
 +  * Suppose we encode streets as labelled graphs, where each label '​r',​ '​g'​ or '​b'​ denotes a street color. These colors can be any alphabetical character, not necessarily just rgb.  
 +  * Given a **start node** and a **sequence of colors**, find all the destination nodes that can be accessed by traversing streets in that particular color. 
 +    * Example: Starting from 0, on the sequence ''​rrg'',​ the destination node are ''​1''​ (0 red to 1 red to 4 green to 1) and ''​3''​ (0 red to 2, red to 2, red to 3) 
 +  * Hint: use **foldLeft** as well as **for expressions**. 
 + 
 +<code scala> 
 +val example = """​0 r 1 
 +                  |0 r 2 
 +                  |0 g 1 
 +                  |1 g 2 
 +                  |1 b 3 
 +                  |1 r 4 
 +                  |4 g 1 
 +                  |3 b 2 
 +                  |2 r 2 
 +                  |2 g 3"""​.stripMargin 
 +            
 +type Streets = Map[(Int,​Char),​Set[Int]] 
 +def readStreets(s:​ String): Streets = ??? 
 + 
 +def findDestination(start:​ Int, colors: String, streets: Streets): Set[Int] = ??? 
 +</​code>​ 
 + 
  
 ===== 2. Python introduction ===== ===== 2. Python introduction =====
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 ==== List traversal ==== ==== List traversal ====
  
-**Exercise ​1.1.** Write a function ''​f(l)''​ which determines the maximum of a list ''​l''​ of integers.+**Exercise ​2.1.** Write a function ''​f(l)''​ which determines the maximum of a list ''​l''​ of integers.
  
 <hidden The pythonic way> ​ <hidden The pythonic way> ​
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 </​hidden>​ </​hidden>​
  
-**Exercise ​1.2.** Modify the previous function to ''​f(l,​start,​stop)''​ and determine the maximum between positions ''​start''​ and ''​stop''​.+**Exercise ​2.2.** Modify the previous function to ''​f(l,​start,​stop)''​ and determine the maximum between positions ''​start''​ and ''​stop''​.
  
 <hidden The pythonic way> ​ <hidden The pythonic way> ​
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 ==== Slicing lists ==== ==== Slicing lists ====
  
-**Exercise ​1.3.** Find the **longest** sequence of positive integers from a list. E.g. for the list ''​[1,​3,​-1,​2,​0,​1,​5,​4,​-2,​4,​5,​-3,​0,​1,​2]''​ the answer is ''​[2,​0,​1,​5,​4]''​.+**Exercise ​2.3.** Find the **longest** sequence of positive integers from a list. E.g. for the list ''​[1,​3,​-1,​2,​0,​1,​5,​4,​-2,​4,​5,​-3,​0,​1,​2]''​ the answer is ''​[2,​0,​1,​5,​4]''​.
  
 <hidden The pythonic way> ​ <hidden The pythonic way> ​
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 </​hidden>​ </​hidden>​
  
-**Exercise ​1.4.** Write a pythonic function to check if a list is palindrome.+**Exercise ​2.4.** Write a pythonic function to check if a list is palindrome.
  
 ===== Other datatypes ===== ===== Other datatypes =====
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 </​code>  ​ </​code>  ​
  
-**Exercise ​1.5.** Write a function which determines (and returns) the **longest** sequence of consecutive integers from a list.+**Exercise ​2.5.** Write a function which determines (and returns) the **longest** sequence of consecutive integers from a list.
  
 ==== Dictionaries ==== ==== Dictionaries ====
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 Example: Example:
 <​code>​ <​code>​
 +5
 0 r 1 0 r 1
 0 r 2 0 r 2
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   * ''​None'':​ represents the lack of a value (or an explicit None value); useful to mark functions which have no return value, or that a value may be purposefully missing (in combination with the ''​|''​ operator), and a None check may be necessary   * ''​None'':​ represents the lack of a value (or an explicit None value); useful to mark functions which have no return value, or that a value may be purposefully missing (in combination with the ''​|''​ operator), and a None check may be necessary
 full documentation of the python typing module: [[https://​docs.python.org/​3/​library/​typing.html]] full documentation of the python typing module: [[https://​docs.python.org/​3/​library/​typing.html]]
 +
 +
 +
 +===== Solutions =====
 +<note important>​
 +[[https://​github.com/​NethDR/​LFA-LAB1-solutions|click here for spoilers/​solutions]]
 +</​note>​