So today i learnt Sieve of Eratosthenes 

the sources that i uses was anuj bhaiyas dsa course its really a interesting one 

and i used geeks for geeks thats also pretty cool trick to figure out the prime  number 

finding  a prime number is relly a tough when the number gets bigger and bigger

SO WHATS DIFFERENT IN IT ??

in it we first take a array of length n (basically its a bollean array so it contains yes or no) intially we make it yes 

then we run a loop from 2-√n  (if we focus here the loop intially is reduced so we save a lots of time ofcourse thats also true if you use ssd)

so now  when we run loop for 1st the value of i(loop varible) which is 2 so we make all the multiples of 2 as false for example in the array the 4th,6th,8th10th...... positions are marked false

now when the i is 3 we make all the multiples of 3 marked as false

for example 6th,9th,12....

thing to note is that we mark all the multiple excepet itself that is (2nd in case of i=2 and 3rd in case of i=3) 

and we keep on doning till i=√n

and finally what we achive is a prime nuber 

for eg

exception initially we mark the first position as false

in this eg we have taken n=12

1st position=false ;2nd position=true ;3rd position=true ; 4th position=true ; 5th position=true ; 6th position=true ; 7th  position=true ;8th  position=true ;9th  position=true ;10th  position=true ;11th  position=true ;12th position=true 

after i=2(or running the loop 1st time)

1st position=false ;2nd position=true ;3rd position=true ; 4th position=false ; 5th position=true ; 6th position=false; 7th  position=true ;8th  position=false ;9th  position=true ;10th  position=false ;11th  position=true ;12th position=false 

after i=2(or running the loop 1st time)

1st position=false ;2nd position=true ;3rd position=true ; 4th position=false ; 5th position=true ; 6th position=false; 7th  position=true ;8th  position=false ;9th  position=false;10th  position=false ;11th  position=true ;12th position=false 

what we get is 

 2nd position=true ;3rd position=true ; 5th position=true ;  7th  position=true;11th  position=true 

here we run loop only 2 times cause √12=3(approx)

so thats the advantage 

we can  find the prime number in a range using this trick 

it can also be applied to find the prime number individually as what we learn in our primary classes of coding

which is the answer

thanks for reading 

PPG