Simplify combineWithoutRepetition algorithm.

Author: trekhleb

src/algorithms/sets/combinations/combineWithoutRepetitions.js

@@ -1,68 +1,37 @@
-/*
-@see: https://stackoverflow.com/a/127898/7794070
-
- Lets say your array of letters looks like this: "ABCDEFGH".
- You have three indices (i, j, k) indicating which letters you
- are going to use for the current word, You start with:
-
- A B C D E F G H
- ^ ^ ^
- i j k
-
- First you vary k, so the next step looks like that:
-
- A B C D E F G H
- ^ ^ ^
- i j k
-
- If you reached the end you go on and vary j and then k again.
-
- A B C D E F G H
- ^ ^ ^
- i j k
+/**
+ * @param{*[]} comboOptions
+ * @param{number} comboLength
+ * @param{*[][]} combos
+ * @param{*[]} currentCombo
+ * @return{*[]}
+ */
+functioncombineRecursively(comboOptions,comboLength,combos=[],currentCombo=[]){
+if(comboLength===0){
+combos.push(currentCombo);
 
- A B C D E F G H
- ^ ^ ^
- i j k
+returncombos;
+}
 
- Once you j reached G you start also to vary i.
+for(letletterIndex=0;letterIndex<=(comboOptions.length-comboLength);letterIndex+=1){
+constletter=comboOptions[letterIndex];
+constrestCombinationOptions=comboOptions.slice(letterIndex+1);
 
- A B C D E F G H
- ^ ^ ^
- i j k
+combineRecursively(
+restCombinationOptions,
+comboLength-1,
+combos,
+currentCombo.concat([letter]),
+);
+}
 
- A B C D E F G H
- ^ ^ ^
- i j k
- ...
- */
+returncombos;
+}
 
 /**
  * @param{*[]} combinationOptions
  * @param{number} combinationLength
  * @return{*[]}
  */
 exportdefaultfunctioncombineWithoutRepetitions(combinationOptions,combinationLength){
-// If combination length is just 1 then return combinationOptions.
-if(combinationLength===1){
-returncombinationOptions.map(option=>[option]);
-}
-
-// Init combinations array.
-constcombinations=[];
-
-for(leti=0;i<=(combinationOptions.length-combinationLength);i+=1){
-constsmallerCombinations=combineWithoutRepetitions(
-combinationOptions.slice(i+1),
-combinationLength-1,
-);
-
-for(letj=0;j<smallerCombinations.length;j+=1){
-constcombination=[combinationOptions[i]].concat(smallerCombinations[j]);
-combinations.push(combination);
-}
-}
-
-// Return all calculated combinations.
-returncombinations;
+returncombineRecursively(combinationOptions,combinationLength);
 }