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Update double_factorial.cpp

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DarkWarrior703 2020-04-25 22:28:20 +03:00 committed by GitHub
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1 changed files with 5 additions and 3 deletions
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math/double_factorial.cpp
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@ -2,13 +2,15 @@
#include <cassert>
/* Double factorial of a non-negative integer n,
is defined as the product of all the integers from 1 to n
is defined as the product of
all the integers from 1 to n
that have the same parity (odd or even) as n.
It is also called as semifactorial of a number and is denoted by !! */
It is also called as semifactorial
of a number and is denoted by !! */
unsigned long long double_factorial_iterative(unsigned int n){
unsigned long long res = 1;
for(unsigned long long i = n; i >= 0; i -= 2){
for( unsigned long long i = n; i >= 0; i -= 2 ){
if(i == 0 || i == 1) return res;
res *= i;
}