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/**
* This program shows the different kinds of calls that can be made for functions like the factorial, and fibonacci
*
*/
public class FactorialExample {
public static void main(String[] args) {
System.out.println( factRecursive(5));
System.out.println( factTailRecursive(5));
System.out.println( factIterative(5));
}
/**
* This is a simple version of factorial function making recursive calls.
* It is not tail recursive, and so cannot be optimized in a functional compiler,
* or be made into an iterative function for compilers like Java & C#.
* @param n - the number to find the factorial for
* @return the factorial of n (assumes positive number, negatives are treated as the value 1)
*/
public static long factRecursive(long n) {
if (n <= 1) {
// base case - keep counting down until this case is reached (assuming positive numbers)
return 1;
}
else {
// recursive call - more work has to be done in the next call
return n * factRecursive(n-1);
}
}
/**
* This is the initial call for the fact2 function. The accumulator is set to 1, and other calls are made
* with the accumulator passed in.
* @param n - the number to find the factorial for
* @return the factorial of n (assumes positive number, negatives are treated as n = 1)
*/
public static long factTailRecursive(long n) {
// set the default value for the accumulator if this is the first call
long accumulator = 1;
if (n <= 1) {
return accumulator;
}
else {
return fact2(n-1, accumulator * n);
}
}
/**
* Iterative call that does not use recursion. It is possible to do this because there is a tail recursive version.
* You can always rewrite tail recursive calls as iterative, and vice versa.
* @param n - the number to find the factorial for
* @return the factorial of n (assumes positive number, negatives are treated as n = 1)
*/
public static long factIterative(long n) {
long acc = 1;
// iterative version
while (n > 1) {
acc = acc * n;
n--;
}
return acc;
}
}
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