Data Structure is a way to organized data in such a way that it can be used efficiently. Following terms are foundation terms of a data structure.
Interface − Each data strucure has an interface. Interface represents the set of operations that a datastructure supports.An interface only provides the list of supported operations, type of parameters they can accept and return type of these operations.
Implementation − Implementation provides the internal representation of a data structure. Implementation also provides the defination of the alogrithms used in the opreations of the data structure.
Correctness − Data Structure implementation should implement its interface correctly.
Time Complexity − Running time or execution time of operations of data structure must be as small as possible.
Space Complexity − Memory usage of a data structure operation should be as little as possible.
As applications are getting complex and data rich, there are three common problems applications face now-a-days.
Data Search − Consider an inventory of 1 million(106) items of a store. If application is to search an item. It has to search item in 1 million(106) items every time slowing down the search. As data grows, search will become slower.
Processor speed − Processor speed although being very high, falls limited if data grows to billon records.
Multiple requests − As thousands of users can search data simultaneously on a web server,even very fast server fails while searching the data.
To solve above problems, data structures come to rescue. Data can be organized in a data structure in such a way that all items may not be required to be search and required data can be searched almost instantly.
There are three cases which are usual used to compare various data structure's execution time in relative manner.
Worst Case − This is the scenario where a particular data structure operation takes maximum time it can take. If a operation's worst case time is ƒ(n) then this operation will not take time more than ƒ(n) time where ƒ(n) represents function of n.
Average Case − This is the scenario depicting the average execution time of an operation of a data structure. If a operation takes ƒ(n) time in execution then m operations will take mƒ(n) time.
Best Case − This is the scenario depicting the least possible execution time of an operation of a data structure. If a operation takes ƒ(n) time in execution then actual operation may take time as random number which would be maximum as ƒ(n).