Introduction to

Data Structure

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Algorithm● An algorithm is a finite set of instructions

which, when followed, accomplishes a particular task.

● Its Characteristics ○ Each instruction should be unique and concise○ Each instruction should be relative in nature

and should not be repeated infinitely.○ Repetition of same task(s) should be avoided.○ The result be available to the user after the

algorithm terminates.

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Efficiency of Algorithms● The performance of algorithms can be

measured on the scales

● Time● Space

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Space Complexity● The amount of memory space required by the

algorithm during the course of execution● Some of the reasons for space complexity are

○ If the program, is to run on mutli-user system, it may be required to specify the amount of memory to be allocated to the program

○ We may be interested to know in advance that whether sufficient memory is available to run the program.

○ There may be several possible solutions with different space requirements.

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Space needed by Program Components

● Instruction Space – Space needed to store the executable version of the program and it is fixed.

● Data Space : It is needed to store all constants, varialbe values

● Environment Space : Space needed to store the information needed to resume the suspended functions.

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Time Complexity● The amount of time needed to run to

completion.● Some reasons for studying time

complexity○ We may be interested to know in

advance that whether a program will provide satisfactory real time response.

○ There must be several possible solutions with different time requirements.

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Data structure ● When elements of data are organized together in

terms of some relationships among the elements, the organization is called data structure.

● A data structure is a set of data values along with the relationship between the data values in form of set of operations permitted on them.

● Arrays, records, stacks, lists, graphs are the names of some of some of these basic data structures.

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A data structure can be(a) transienti.e. it is created when a program starts and is destroyed when the program ends. Most data structures in main memory are transient, for example, an array of data.

(b) Permanenti.e. it already exists when a program starts and is preserved when the program ends. Most data structures on disk are permanent, for example, a file of data, or a cross-linked data file collection (a database).

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Data Structure

Linear Non-Linear

● Array● Stack● Queue● Linked

Lists

● Tree● Graph

Abstract Data Type (ADT)● It is a mathematical model with a collections of

operations defined on that model.

● The ADT encapsulates a data type can be localized and are not visible to the users of the ADT.

● An implementation of an ADT is a translation into statements of a programming language, of the declaration that defines a variable to be of that ADT, plus a procedure in that language for each operation of the ADT.

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