Factorial¶

Query Source: adopted from here

Introduction¶

Factorial is one of most common mathematical concepts, which is the product of all positive integers less than or equal to $n$ . It is denoted mathematically as,

$n! = n \times (n-1) \times (n-2) \times \cdot\cdot\cdot \times 1$

This is commonly seen in combinations and permutations or Taylor series.

Question¶

Implement a function factorial to calculate the factorial of a given integer. Return zero if the input integer is negative. Try your best to provide multiple implementations.

Answer¶

Below are a couple of suggested implementations:

Method 1: Use prd

factorial:{$[x<0;0;prd 1+til x]};

Method 2: Use recursive function

factorial:{$[x<0;0;x=0;1;x*.z.s x-1]};

Method 3: Use over

factorial:{$[x<0;0;(*/)1+til x]};

Method 4: Use do

factorial:{do[-1+current:result:x;result*:current-:1];$[result<0;0;1|result]};