1.
Abstract Data Types:
Lists

2.
List
• A List is a sequence of zero or
more elements.
a1, a2, a3, a4, ………..,an
Where n  0,
a1 is the first element
an is the last element
n is length of the list
if n = 0, the list is empty (no
element)
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3.
More about lists
• Elements are linearly ordered.
ai precedes ai+1
for i = 1, 2, 3,… (n-1)
ai follows ai-1
for i = 2, 3,… n
• Element ai is at position i
a1, a2, a3, a4, ………..,an
Not a list
a1, a3, a5, a7, ………..,an
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1 2 3 4 n Position of
element.

4.
More about lists
a1, a2, a3, a4, a5
a1, a2, a3, a4, a5, a6, a7
a1, a2, a3, a4
a1, a2, a3
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5.
LIST: Abstract Data Type
• L: List of elements
• e: an element
• p: position
LIST ADT
Properties
- Sequence of linearly
ordered elements.
Operations
• Insert(e, p, L)
• Locate(e,L)
• Retrieve(p,L)
• Delete(p,L)
• Next(p,L)
• Previous(p,L)
• MakeNull(L)
• First(L)
• PrintList(L)
• END(L)
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6.
Print all elements of the LIST ADT
• PRINTLIST(L)
• Print the elements of L in order of occurrence.
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7.
End of list
a1, a2, a3, a4 ,…………, an
• END(L)
• Returns the position following an on the list.
a1, a2, a3, a4, a5, a6, a7
• END(L) will return 8 for this list
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1 2 3 4 7 Position of element.

8.
First position on LIST ADT
a1, a2, a3, a4 ,…………, an
• FIRST(L)
• Returns the first position on the list.
• If L is empty the position returned is END(L)
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1 2 3 4 n Position of element.

9.
Next and Previous position on LIST ADT
• NEXT(p, L)
• Returns the position following the position p on the list.
• PREVIOUS(p, L)
• Returns the position preceding the position p on the list.
• If p is the last position on the list then NEXT(p,L) will return END(L).
• PREVIOUS is undefined if p is 1.
• Both functions are undefined if L has no position p.
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10.
Insert an element in LIST ADT
a1, a2, a3, a4, a5, a6, a7
• INSERT(e, p, L)
a1, a2, a3, a4 ,……ap ,…… an
a1, a2, a3, a4 ,……,ap-1, e, ap ,…… an
• INSERT(3, 5, a1, a2, a3, a4, a5, a6, a7)
a1, a2, a3, a4, a5, a6, a7
a1, a2, a3, a4, 3, a5, a6, a7
• if p = END(L) then L becomes a1, a2, a3, a4, a5, a6, a7, e
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11.
Locate an element in LIST ADT
33, 90, 76, 21, 65, 36, 87
• LOCATE(e, L)
• Returns the position of e on list L
• LOCATE(76,L)
• Return 3
• If e appears more than once, then the position of first occurrence is
returned.
• If e does not appear than END(L) is returned.
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1 2 3 4 7 Position of element.

12.
Retrieve an element from LIST ADT
33, 90, 76, 21, 65, 36, 87
• Retrieve(p, L)
• Returns the element at position p from the List.
• Retrieve(3, L) will return 76
• The result is undefined if p = END(L) or if L has no position p
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1 2 3 4 7 Position of element.

13.
Delete an element from the list
a1, a2, a3, a4, a5, a6, a7
• DELETE(p, L)
a1, a2, a3, a4 ,……ap ,…… an
a1, a2, a3, a4 ,……,ap-1, ap+1 ,…… an
• DELETE(5, L)
a1, a2, a3, a4, a5, a6, a7
a1, a2, a3, a4, a6, a7
• Result is undefined if L has no position p
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14.
Empty entire LIST ADT
• MAKENULL(L)
• L becomes empty and returns position END(L)
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15.
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