Lecture 02: List Array Implementation

Overview:

  1. List ADT
  2. SimpleList interface
  3. Array Imp
  4. Linked List Imp
  5. Comparison of Imps
  6. Other ADTs: Stack, Queue, Deque

Logistics:

  • TA session: M, W 7-9pm A131 or by zoom
  • Assignment 1 due Sep 14

I. List ADT (lec01)

The state of a list is a sequence of n elements. S: x~0~, x~1~ … x~i-1~, x~i~ … x~n-1~ [n elements] Operations:

  • size() - return num of elements
  • isEmpty() - return (n==0)
  • get(i) - return \(x_i\) (0 ≤ i ≤ n-1)
  • set(i, y) - update state to \(x_0, x_1 \ldots x_{i-1}, y, x_{i+1} \ldots x_{n-1}\) (0 ≤ i ≤ n-1)
  • add(i, y) - update state to \(x_0, x_1 \ldots x_{i-1}, y, x_{i} \ldots x_{n-1}\) [new size n+1]
  • remove(i) - update state to \(x_0, x_1 \ldots x_{i-1}, x_{i+1} \ldots x_{n-1}\) [new size n-1]

Notice: after add & remove, the subscript no longer agree with the original index.

II. Example SimpleList interface

Java interface - specifies required functionality of an implementation (specify WHAT but not HOW) comments - specifies interpretation of operations parameterized data type E (see prof’s code).

III. Array Implmentation

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3

Object[] contents = new Object [10]; // create fixed sized array
contents[3] // access item @ idx 3 
contents[3] = value; // sets value of item @ idx 3

Store elements of list in array; maintain that x~0~, x~1~ …x~n-1~ are stored consecutively in contents.

Suggestion: separate size of list and capacity of array. Store

  • Object[] contents
  • int size = # elts in list

| 0 | 1 | 2 | 3 | 4 | 5 | NA | NA | list size 6, capacity 8

How to implement size? return size; (make sure size is always correct / updated)

How to imp isEmpty? return size == 0; only assumes size is correct. ` return contents[0] == null;` assumes “null” is not a valid entry in List.

How to get(i)?

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check i is valid 0 ≤ i ≤ size()-1
return contents[i];

How to set(i, x)?

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2

check i is valid 0 ≤ i ≤ size()-1
return contents[i] = x;

How to add(i, x)?

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copy and set 
increment size

How to remove(i, x)?

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copy and set
decrement size