moved from memoization to dp implementation of factorials

src/main/math.js

@@ -14,35 +14,35 @@
  * An array containing the currently calculated factorials.
  * 
  * Note that given an index i, `factorials[i] contains i!`.
- * E.g.
+ * e.g.
  * - factorials[0] = 0! = 1
  * - factorials[5] = 5! = 120
  * - ...
  */
-const _factorials = [
-    1, 1, 2, 6, 24, 120, //0!..5!
-    720, 5040, 40320, 362880, 3628800, //6!..10!
-    39916800, 479001600, 6227020800, 87178291200, 1307674368000, //11!..15!
-    20922789888000, 355687428096000, 6402373705728000, 121645100408832000, 2432902008176640000 //16!..20!
-];
+const _factorials = new Array(170);
 
 /**
- * Returns the factorial of `value`. If `value > 170`, `Infinity` is returned.
+ * Returns the factorial of `value`. 
+ * If `value > 170`, `Infinity` is returned.
  * 
  * Note that `no type checks` are done on `value`.
  * @param {number} value The number to calculate the factorial of.
  * @returns {number} The factorial of `value`.
  */
 export const FACTORIAL = (value) => {
-    let _fact = _factorials[value];
+    if (_factorials[value]) return _factorials[value];
+    if (value > 170) return Infinity;
+    if (value == 0) return 1;
 
-    if (!_fact) {
-        _fact = value * FACTORIAL(value - 1);
-        _factorials[value] = _fact;
+    let _fact = 1;
+    for (let i = 1; i <= value; i++) {
+        _fact *= i;
+        _factorials[i] = _fact;
     }
-
     return _fact;
 }
+FACTORIAL(170); //Forcefully cache the factorials
+Object.seal(_factorials);
 
 /**
  * Checks whether `value` is a positive number (i.e. > 0).