Dear students, welcome to GATE SMASHERS In this video I am going to explain the concept of hashing So all the important points related to
hashing I will explain to you in this video Hashing is if we talk about competitive exams So like GATE exam, NET exam, different PSUs Every exam contains at least one to
two questions from the hashing And it is a very simple topic but it is important Even it is very important for your college and university exams So I will give you at least 2-3 videos on hashing
so that I can tell you the whole concept So guys like the video quickly and subscribe the channel If you haven't done it yet and if you have done it Then you can get it subscribed from other devices by sharing because subscribers are very important So let's start If we talk about hashing, then what is it actually? It is a method for storing and retrieving the
data from database in order of one time Means we are storing data in constant
time and retrieving it from the database It is also called mapping technique Because we try to map larger values into
smaller values by using the concept of hashing Now in hashing, what are the terms that come? So first comes search key You are told that these are search
keys, put them in the hash table So what is the search key? We search on
the basis of some key in the database Like if we take the student's data, we
put role number or registration number In the data of passport, we put it in the passport number So there is some search key on which we store the data So where do we put those search keys? We have to put it in the hash table So what are the keys? They will be given to you in the maximum question Sometimes we can put the record too there is a lot in record, in database record there is the student's name, father's name, mother's name If you don't put all these values in the hash
table, then what will you put? Search Key If we talk about the hash table, what is the hash table? It is a data structure that actually provides you a methodology that you can store the data properly And what is this in a way? It is an array type Like our indexes are in the array, there are indexes in this too But when we have to search or insert or delete any data in this Then we don't need to scan it, with the help of hash
function we will do this in order of one time I will tell you from the example If we talk about such hash functions, then K mod N, K mod N, mid square method, folding method, different methods But these two methods are used the most So see, first came 24 I have a key and let's say I have
taken this function K mod 10 Which hash function I took? K mod 10 Now I will map this key from this function, where will this go? So to do this, you have to do what is the key value? 24 So 24 mod 10, what to do? 24 mod 10 If you divide any value from 10, then the
remainder will come, that is what? Mod value So see the remainder, what will come? 4 So you got its hash value, what did you get? You got the hash value, means you go
to the 4th number index and put 24 Simple, if you have given K mod N, then the
value of N will be that you have this number of keys The number of keys will be 0 to N-1, you make a table of it If you have given K mod 10, then you have made a table of 0 to 9 Let's say mid-square, what is mid-square?
Listen to this method, sometimes it comes in theory Like if you have given 123, then what you have to do is take the mid-value square and store the data there Similarly, you are given folding many
times, let's say I have data 123456 Now I have to store this much data and
let's say the table I have is between 0 to 999 Now this data will not come in it, so what you have to do is Fold 123456, you have added 123,
separated 4 and 5, 6 separately You have added these two, 9, 7, 5 So you can put this value in this location and store it So there are different methods but remember
these methods are the main ones Next is 52, so 52 mod 10, what will come? 2, done Next what will come? 91 mod 10, what will be the answer? 1 Because what will be the remainder? 67, 67 went to 7th position 48 went to this place and 83 went to 3rd location So your insertion is in order of 1 time, why? Because you have to just calculate the value and on the basis of that you can
put that value in the hash table Now you have to search, so what
you have to do while searching? Same way, let's say you want to search for 67, so you will do 67 mod 10, what will be the answer? 7 So means you have to go to index number 7 and pick up that value And if you have to pick up a record of that
value then it must be in the database If it is in disk then pick it up, so this
pointer will point the database ahead It will be used like an index, so insertion in order of 1 time You have to do deletion also, so search the same value Delete the data from which index you want to go So all the operations will be completed in order of 1 time So this is a simple concept of hashing Next we will talk here, if let's say you are
thinking in the mind of many students That sir let's say data is 62,
62 mod 10, what will be the answer? 2 2 data is there, so in 2 already 52 is
there, so where will you insert 62? This is called concept of collision, when collision occurs in hash table Then how we resolve the collisions, we will
discuss all those methods in the next video Thank You.
