Added factorial method to API

Author: met4citizen

README.md

@@ -257,6 +257,7 @@ FUNCTION| DESCRIPTION
 <nobr>`set(key,value)`</nobr> | Set option. Currently supports the following keys: `observer` (1=quantum, 2=classic), `maxcliquesperloc` (number) and `maxstatesperclique` (number).
 <nobr>`get(key)`</nobr> | Get option value.
 <nobr>`clone(x)`</nobr> | Makes a deep copy of the given data structure.
+<nobr>`factorial(x)`</nobr> | Factorial of `x`.
 <nobr>`shuffle(arr)`</nobr> | Shuffles an array in place using the Fisher-Yates shuffle.
 <nobr>`*comb(arr,[size])`</nobr> | Generates all combinations of a set. `size` is the length of the combination. An example:<br/>`comb([a,b,c],2)` -> `[a,b] [a,c] [b,c]`
 <nobr>`*perm(arr,[size])`</nobr> | Generates all permutations of a set. `size` is the length of the permutation. An example:<br/>`perm([a,b,c],2)` -> `[a,b] [a,c] [b,a] [b,c] [c,a] [c,b]`

lib/ModelAPI.js

@@ -14,6 +14,7 @@ class ModelAPI {
   constructor() {
     this._id = 0;
     this._opt = {};
+    this._fmem = [BigInt(0), BigInt(1)]; // Factorial memoization
   }
 
   /**
@@ -51,6 +52,18 @@ class ModelAPI {
     return JSON.parse(JSON.stringify(o));
   }
 
+  /**
+	* Factorial with BigInt and memoization.
+	* @param {bigint} n
+	* @return {bigint} n!
+	*/
+	factorial(n) {
+    while( this._fmem.length <= n ) {
+      this._fmem.push( this._fmem[ this._fmem.length-1 ] * BigInt( this._fmem.length ) );
+    }
+    return BigInt( this._fmem[n] );
+	}
+
   /**
   * Generates all combinations of a set.
   *   comb([a,b,c],2) -> [a,b] [a,c] [b,c]

server/api.mjs

@@ -14,6 +14,7 @@ class ModelAPI {
   constructor() {
     this._id = 0;
     this._opt = {};
+    this._fmem = [BigInt(0), BigInt(1)]; // Factorial memoization
   }
 
   /**
@@ -51,6 +52,18 @@ class ModelAPI {
     return JSON.parse(JSON.stringify(o));
   }
 
+  /**
+  * Factorial with BigInt and memoization.
+  * @param {bigint} n
+  * @return {bigint} n!
+  */
+  factorial(n) {
+    while( this._fmem.length <= n ) {
+      this._fmem.push( this._fmem[ this._fmem.length-1 ] * BigInt( this._fmem.length ) );
+    }
+    return BigInt( this._fmem[n] );
+  }
+
   /**
   * Generates all combinations of a set.
   *   comb([a,b,c],2) -> [a,b] [a,c] [b,c]