package modernjavainaction.chap18;

import java.util.stream.LongStream;

public class Recursion {

  public static void main(String[] args) {
    System.out.println(factorialIterative(5));
    System.out.println(factorialRecursive(5));
    System.out.println(factorialStreams(5));
    System.out.println(factorialTailRecursive(5));
  }

  public static int factorialIterative(int n) {
    int r = 1;
    for (int i = 1; i <= n; i++) {
      r *= i;
    }
    return r;
  }

  public static long factorialRecursive(long n) {
    return n == 1 ? 1 : n * factorialRecursive(n - 1);
  }

  public static long factorialStreams(long n) {
    return LongStream.rangeClosed(1, n).reduce(1, (long a, long b) -> a * b);
  }

  public static long factorialTailRecursive(long n) {
    return factorialHelper(1, n);
  }

  public static long factorialHelper(long acc, long n) {
    return n == 1 ? acc : factorialHelper(acc * n, n - 1);
  }

}
