Lecture No. 02
Reading Material
Data Structures and Algorithm Analysis in C++ Chapter. 3
3.1, 3.2, 3.2.1, 3.2.2
Summary
1) List Implementation
• add Method
• next Method
• remove Method
• find Method
• Other Methods
2) Analysis Of Array List
3) List Using Linked Memory
4) Linked List
Today, we will discuss the concept of list operations. You may have a fair idea of ‘ start operation’ that sets the current pointer to the first element of the list while the tail operation moves the current pointer to the last element of the list. In the previous lecture, we discussed the operation next that moves the current pointer one element forward. Similarly, there is the ‘back operation’ which moves the current pointer one element backward.
List Implementation
Now we will see what the implementation of the list is and how one can create a list in C++. After designing the interface for the list, it is advisable to know how to implement that interface. Suppose we want to create a list of integers. For this purpose, the methods of the list can be implemented with the use of an array inside. For example, the list of integers (2, 6, 8, 7, 1) can be represented in the following
12
CS301 – Data Structures
manner where the current position is 3.
A
2
6
8
7
1
current
size
1
2
3
4
5
3
5
In this case, we start the index of the array from 1 just for simplification against the usual practice in which the index of an array starts from zero in C++. It is not necessary to always start the indexing from zero. Sometimes, it is required to start the indexing from 1. For this, we leave the zeroth position and start using the array from index 1 that is actually the second position. Suppose we have to store the numbers from 1 to 6 in the array. We take an array of 7 elements and put the numbers from the index 1. Thus there is a correspondence between index and the numbers stored in it. This is not very useful. So, it does not justify the non-use of zeroth position of the array out-rightly. However for simplification purposes, it is good to use the index from 1.
add Method
Now we will talk about adding an element to the list. Suppose there is a call to add an element in the list i.e. add(9). As we said earlier that the current position is 3, so by adding the element 9 to the list, the new list will be (2, 6, 8, 9, 7, 1).
To add the new element (9) to the list at the current position, at first, we have to make space for this element. For this purpose, we shift every element on the right of 8 (the current position) to one place on the right. Thus after creating the space for new element at position 4, the array can be represented as
We have moved the current position to 4 while increasing the size to 6. The size shows that the elements in the list. Where as the size of the array is different that we have defined already to a fixed length, which may be 100, 200 or even greater.
next Method
Now let’s see another method, called ‘next’. We have talked that the next method moves the current position one position forward. In this method, we do not add a new element to the list but simply move the pointer one element ahead. This method is required while employing the list in our program and manipulating it according to the requirement. There is also an array to store the list in it. We also have two variables- current and size to store the position of current pointer and the number of elements in the list. By looking on the values of these variables, we can find the state of the list
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