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This document from wellesley college's cs111 computer programming course covers the topic of lists represented as intlists. The concept of box-and-pointer notation, the usefulness of lists, and five core intlist methods: isempty, head, tail, prepend, and empty. The document also includes examples of constructing intlists using empty() and prepend() methods, as well as sharing list nodes and recursive list methods such as sumlist, length, maxlist, and areallpositive.
Typology: Study notes
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Lists 14-
IntLists are defined recursively:
An IntList is either
head 8 tail
head 11 tail
head- tail
IntList IntList IntList IntList
empty
// list node // list node // list node // empty list
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Box-and-pointer notation
We represent list nodes and empty lists using a shorthand known as box-and-pointer notation.
head 8 tail
head 11 tail
head- tail
IntList IntList IntList IntList
empty
8 11 -2 Ø
// list node // list node // list node // empty list
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Why are lists useful?
91 0 -22 ... (^38) Ø
list
21 91 0 ... (^38) Ø
list
21
list
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isEmpty method
public static boolean isEmpty (IntList L) Returns true if L is an empty integer list and false if L is an integer list node.
list list list
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head method
public static int head (IntList L) Returns the integer that is the head component of the integer list node L. Signals an exception if L is empty.
list list list
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tail method
public static IntList tail (IntList L) Returns the integer list that is the tail component of the integer list node L. Signals an exception if L is empty.
list list list
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heads and tails
list list list
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Sharing list nodes
list4^4
IntList list4 = IntList.prepend(4, IntList.prepend(3, IntList.prepend(2, IntList.prepend(1, IntList.empty()))));
IntList list5 = IntList.prepend(7, IntList.prepend(4, IntList.tail(IntList.tail(list4))));
list5 7 4 list6 8
IntList list6 = IntList.prepend(8, IntList.tail(list5));
Lists 14-
Recursive list methods
Lists 14-
Recursive list methods
Lists 14-
Recursive list methods
Lists 14-
Squaring numbers
o Method mapSquares(IntList L) returns a list, such that each element in the list is the “square” of the corresponding element in “L”. o For example, mapSquares(L)
Lists 14-
mapSquares(IntList L);
// Returns a new list whose elements are the sqaures of // the corresponding elements in the given list public static IntList mapSquares(IntList L) {
if ( ) { // base case return } else { // recursive case return
Lists 14-
mapSquares(IntList L);
// Returns a new list whose elements are the sqaures of // the corresponding elements in the given list public static IntList mapSquares(IntList L) {
if ( InList.isEmpty(L) ) { // base case return empty(); } else { // recursive case return IntList.prepend(IntList.head(L)*IntList.head(L), mapSquares(IntList.tail(L))); } }
Lists 14-
Filter methods
Afilter method passes some elements through and holds other elements back.
More formally: Afilter method transforms one list to another by keeping only those elements satisfying a given predicate.
L1 L
filter
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filterEven(IntList L);
// Returns sublist containing elements of L that are even public static IntList filterEven(IntList L) {
if ( IntList.isEmpty(L) ) { // base case return IntList.empty(); } else if ( (IntList.head(L) % 2) == 0 ) { // recursive case return IntList.preprend(IntList.head(L), filterEven(IntList.tail(L))); } else { return filterEven(IntList.tail(L)); } }
