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feat: updated the Prime number checking code to make it more efficient (#1714)

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* updated the code to make it more efficient

* Update math/check_prime.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Update math/check_prime.cpp

Co-authored-by: David Leal <halfpacho@gmail.com>

* Apply suggestions from code review

Co-authored-by: David Leal <halfpacho@gmail.com>
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OM GUPTA 2021-10-22 17:07:33 +05:30 committed by GitHub
parent 5b78538570
commit 6c6747174c
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1 changed files with 11 additions and 10 deletions
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math/check_prime.cpp
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@ -7,12 +7,13 @@
* @brief
* Reduced all possibilities of a number which cannot be prime.
* Eg: No even number, except 2 can be a prime number, hence we will increment
* our loop with i+2 jumping on all odd numbers only. If number is <= 1 or if it
* is even except 2, break the loop and return false telling number is not
* prime.
* our loop with i+6 jumping and check for i or i+2 to be a factor of the number;
* if it's a factor then we will return false otherwise true after the loop terminates at the terminating condition which is (i*i<=num)
*/
#include <cassert>
#include <iostream>
#include <cassert> /// for assert
#include <iostream> /// for IO operations
/**
* Function to check if the given number is prime or not.
* @param num number to be checked.
@ -23,14 +24,14 @@ bool is_prime(T num) {
bool result = true;
if (num <= 1) {
return false;
} else if (num == 2) {
} else if (num == 2 || num==3) {
return true;
} else if ((num & 1) == 0) {
} else if ((num%2) == 0 || num%3 == 0) {
return false;
}
if (num >= 3) {
for (T i = 3; (i * i) <= (num); i = (i + 2)) {
if ((num % i) == 0) {
else {
for (T i = 5; (i * i) <= (num); i = (i + 6)) {
if ((num % i) == 0 || (num%(i+2)==0 )) {
result = false;
break;
}