Module 1 notes of data warehousing and data

Asymptotic Analysis:
 The efficiency of an algorithm depends on the amount of
time, storage and other resources required to execute the
algorithm.
 The efficiency is measured with the help of asymptotic
notations.
 An algorithm may not have the same performance for
different types of inputs. With the increase in the input
size, the performance will change.
 Time and Space Complexity in Algorithms - Coding Ninjas CodeStudio

 Asymptotic Notations
 Asymptotic notations are the mathematical notations used to describe
the running time of an algorithm.
 For example: In bubble sort, when the input array is already sorted, the
time taken by the algorithm is linear i.e. the best case.
 But, when the input array is in reverse condition, the algorithm takes
the maximum time (quadratic) to sort the elements i.e. the worst case.
 When the input array is neither sorted nor in reverse order, then it takes
average time.
 These durations are denoted using asymptotic notations.

There are mainly three asymptotic
notations:
•Big-O notation
•Omega notation
•Theta notation

Big-O Notation (O-notation)
Big-O notation represents the upper bound
of the running time of an algorithm. Thus, it gives
the worst-case complexity of an algorithm.

o The below expression can be described as a
function f(n) belongs to the set O(g(n)) if there exists a
positive constant c
such that it lies between 0 and cg(n), for sufficiently large n.
• For any value of n, the running time of an algorithm does not
cross the time provided by O(g(n)).
Since it gives the worst-case running time of an algorithm, it is
widely used to analyze an algorithm as we are always
interested in the worst-case scenario.
O(g(n)) = { f(n): there exist positive constants c and n0
such that 0 ≤ f(n) ≤ cg(n) for all n ≥ n0 }

Omega Notation (Ω-notation)
Omega notation represents the lower bound of the running time of an
algorithm. Thus, it provides the best case complexity of an algorithm.

Ω(g(n)) = { f(n): there exist positive constants c and n0 such that
0 ≤ cg(n) ≤ f(n) for all n ≥ n0 }
The above expression can be described as a function f(n) belongs to
the set Ω(g(n)) if there exists a positive constant c such that it lies
above cg(n), for sufficiently large n.
For any value of n, the minimum time required by the algorithm is given
by Omega Ω(g(n)).

Theta Notation (Θ-notation)
Theta notation encloses the function from
above and below. Since it represents the upper and
the lower bound of the running time of an algorithm,
it is used for analyzing the average-case complexity
of an algorithm.

Θ(g(n)) = { f(n): there exist positive constants c1, c2 and n0
such that 0 ≤ c1g(n) ≤ f(n) ≤ c2g(n) for all n ≥ n0 }
The above expression can be described as a function f(n) belongs to
the set Θ(g(n)) if there exist positive constants c1
and c2 such that it can be sandwiched between c1g(n) and c2g(n), for sufficiently
large n.
If a function f(n) lies anywhere in between c1g(n) and c2g(n) for all n ≥ n0, then f(n) is
said to be asymptotically tight bound.

Algorithm Complexity
• Suppose X is treated as an algorithm and N is treated as the size of
input data, the time and space implemented by the Algorithm X are
the two main factors which determine the efficiency of X.
• Time Factor − The time is calculated or measured by counting the
number of key operations such as comparisons in sorting
algorithm.
• Space Factor − The space is calculated or measured by counting
the maximum memory space required by the algorithm.
The complexity of an algorithm f(N) provides the running time and / or
storage space needed by the algorithm with respect of N as the size
of input data.

Space Complexity
Space complexity of an algorithm represents the amount of memory
space needed the algorithm in its life cycle.
Space needed by an algorithm is equal to the sum of the following two
components
 A fixed part that is a space required to store certain data and
variables (i.e. simple variables and constants, program size etc.),
that are not dependent of the size of the problem.
 A variable part is a space required by variables, whose size is totally
dependent on the size of the problem. For example, recursion stack
space, dynamic memory allocation etc.
 Space complexity S(p) of any algorithm p is S(p) = A + Sp(I) Where
A is treated as the fixed part and S(I) is treated as the variable part of
the algorithm which depends on instance characteristic I. Following
is a simple example that tries to explain the concept

Here we have three variables P, Q and R and one
constant. Hence S(p) = 1+3. Now space is
dependent on data types of given constant types
and variables and it will be multiplied accordingly.
SUM(P, Q)
Step 1 – START
Step 2 - R ← P + Q + 10
Step 3 - Stop

Time Complexity
 Time Complexity of an algorithm is the representation of
the amount of time required by the algorithm to execute
to completion.
 Time requirements can be denoted or defined as a
numerical function t(N), where t(N) can be measured as
the number of steps, provided each step takes constant
time.
 For example, in case of addition of two n-bit integers, N
steps are taken. Consequently, the total computational
time is t(N) = c*n, where c is the time consumed for
addition of two bits. Here, we observe that t(N) grows
linearly as input size increases.

There are five types of Time complexity Cases:
1.Constant Time Complexity - O(1)
2.Logarithmic Time Complexity - O(log n)
3.Linear Time Complexity - O(n)
4.O(n log n) Time Complexity
5.Quadratic Time Complexity - O(n2)

Module 1 notes of data warehousing and data

Arrays
•An array is a data structure used to process multiple
elements with the same data type when a number of
such elements are known.
•It provides a powerful feature and can be used as such
or can be used to form complex data structures like
stacks and queues.
•An array can be defined as an infinite collection of
homogeneous(similar type) elements.
•Arrays are always stored in consecutive memory
locations.

Types of Arrays
There are two types of Arrays
•One Dimensional Arrays
•Two Dimensional Arrays
Multidimensional arrays
A multidimensional array associates each element
in the array with multiple indexes.
The most commonly used multidimensional array is
the two-dimensional array, also known as
a table or matrix. A two-dimensional array
associates each of its elements with two indexes.

2]={0,1,2,3,4,5,6,7,8,9,3,2}
In this type of declaration,
we have an array of type integer,
block size is 3,
row size is 2, column size is 2 and we have mentioned the values
inside the curly braces during the declaration of array.
So all the values will be stored one by one in the array cells.
int arr[3][2][2]={0,1,2,3,4,5,6,7,8,9,3,2}
block(1) 0 1 block(2) 4 5 block(3) 8 9
2 3 6 7 3 2
2x2 2x2 2x2

Dynamic Memory Allocation
 Since C is a structured language, it has some
fixed rules for programming.
 One of them includes changing the size of an
array. An array is a collection of items stored at
contiguous memory locations.

Dynamic Memory Allocation can be defined as a
procedure in which the size of a data structure (like
Array) is changed during the runtime.
C provides some functions to achieve these tasks. There
are 4 library functions provided by C defined
under <stdlib.h> header file to facilitate dynamic
memory
1.malloc()
2.calloc()
3.free()
4.realloc()

 The “malloc” or “memory allocation” method in C is used to
dynamically allocate a single large block of memory with the
specified size.
 It returns a pointer of type void which can be cast into a pointer of
any form. It doesn’t Initialize memory at execution time so that it
has initialized each block with the default garbage value initially.
Syntax:
ptr = (cast-type*) malloc(byte-size)
For Example:
ptr = (int*) malloc(100 * sizeof(int));
 Since the size of int is 4 bytes, this statement will allocate 400
bytes of memory.
 And, the pointer ptr holds the address of the first byte in the
allocated memory.

C calloc() method
1.“calloc” or “contiguous allocation” method in C
is used to dynamically allocate the specified number
of blocks of memory of the specified type. it is very
much similar to malloc() but has two different points
and these are:
2.It initializes each block with a default value ‘0’.
3.It has two parameters or arguments as compare to
malloc().
Syntax:

ptr = (cast-type*)calloc(n, element-size);
here, n is the no. of elements and element-
size is the size of each element.
For Example:
ptr = (float*) calloc(25, sizeof(float));
This statement allocates contiguous space in memory for
25 elements each with the size of the float.

C free() method
“free” method in C is used to dynamically de-
allocate the memory. The memory allocated using
functions malloc() and calloc() is not de-allocated on
their own. Hence the free() method is used, whenever
the dynamic memory allocation takes place. It helps to
reduce wastage of memory by freeing it.
Syntax:
free(ptr);

• “realloc” or “re-allocation” method in C is used to
dynamically change the memory allocation of a
previously allocated memory.
• In other words, realloc can be used to dynamically re-
allocate memory. re-allocation of memory maintains the
already present value and new blocks will be initialized
with the default garbage value.
Syntax:
ptr = realloc(ptr, newSize); where ptr is
reallocated with new size 'newSize'.

Basic Operations:
Following are the basic operations supported by an
array.
•Traverse − print all the array elements one by one.
•Insertion − Adds an element at the given index.
•Deletion − Deletes an element at the given index.
•Search − Searches an element using the given index
or by the value.
•Update − Updates an element at the given index.
Memory Allocations in Data Structures || CseWorld Online

Module 1 notes of data warehousing and data

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