update from Atlas

operator/factorial/CorrectFactorial.java

@@ -0,0 +1,49 @@
+import java.math.BigInteger;
+
+class CorrectFactorial {
+    static final BigInteger two = new BigInteger("2");
+
+    public static BigInteger factorial(BigInteger n) {
+        return n.compareTo(two) < 0 ? BigInteger.ONE
+                    : n.multiply(factorial(n.subtract(BigInteger.ONE)));
+    }
+
+    public static void main(String args[]) {
+        BigInteger upperBound = new BigInteger("25"); 
+        for (BigInteger i = BigInteger.ONE;
+                i.compareTo(upperBound) <= 0;
+                i = i.add(BigInteger.ONE)) {
+            System.out.println(i + "! = " + factorial(i));
+        }
+    }
+}
+
+/* output:
+
+1! = 1
+2! = 2
+3! = 6
+4! = 24
+5! = 120
+6! = 720
+7! = 5040
+8! = 40320
+9! = 362880
+10! = 3628800
+11! = 39916800
+12! = 479001600
+13! = 6227020800
+14! = 87178291200
+15! = 1307674368000
+16! = 20922789888000
+17! = 355687428096000
+18! = 6402373705728000
+19! = 121645100408832000
+20! = 2432902008176640000
+21! = 51090942171709440000
+22! = 1124000727777607680000
+23! = 25852016738884976640000
+24! = 620448401733239439360000
+25! = 15511210043330985984000000
+
+*/

operator/factorial/SimpleFactorial.java

@@ -0,0 +1,43 @@
+class SimpleFactorial {
+
+    public static long factorial(long n) {
+        return n < 2 ? 1 : n * factorial(n-1);
+    }
+
+    public static void main(String args[]) {
+        for (long i = 1; i <= 25; i++) {
+            System.out.println(i + "! = " + factorial(i));
+
+        }
+    }
+}
+
+/* output: ncorrect results starting with 21!
+
+1! = 1
+2! = 2
+3! = 6
+4! = 24
+5! = 120
+6! = 720
+7! = 5040
+8! = 40320
+9! = 362880
+10! = 3628800
+11! = 39916800
+12! = 479001600
+13! = 6227020800
+14! = 87178291200
+15! = 1307674368000
+16! = 20922789888000
+17! = 355687428096000
+18! = 6402373705728000
+19! = 121645100408832000
+20! = 2432902008176640000
+21! = -4249290049419214848
+22! = -1250660718674968576
+23! = 8128291617894825984
+24! = -7835185981329244160
+25! = 7034535277573963776
+
+*/

operator/factorial/factorial.py

@@ -0,0 +1,36 @@
+def factorial(n):
+    return 1 if n < 2 else n * factorial(n-1)
+
+if __name__=='__main__':
+    for i in range(1, 26):
+        print('%s! = %s' % (i, factorial(i)))
+
+"""
+output:
+
+1! = 1
+2! = 2
+3! = 6
+4! = 24
+5! = 120
+6! = 720
+7! = 5040
+8! = 40320
+9! = 362880
+10! = 3628800
+11! = 39916800
+12! = 479001600
+13! = 6227020800
+14! = 87178291200
+15! = 1307674368000
+16! = 20922789888000
+17! = 355687428096000
+18! = 6402373705728000
+19! = 121645100408832000
+20! = 2432902008176640000
+21! = 51090942171709440000
+22! = 1124000727777607680000
+23! = 25852016738884976640000
+24! = 620448401733239439360000
+25! = 15511210043330985984000000
+"""