From f08fc37dad3f4e7d9dcceb8cdcbf07d89859d2ac Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Fri, 4 Jan 2019 17:03:35 +0200
Subject: [PATCH] Add comments to combination algorithms.

---
 .../sets/combinations/combineWithRepetitions.js           | 8 ++++++--
 .../sets/combinations/combineWithoutRepetitions.js        | 8 ++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/algorithms/sets/combinations/combineWithRepetitions.js b/src/algorithms/sets/combinations/combineWithRepetitions.js
index 8a743289..0c3df4ec 100644
--- a/src/algorithms/sets/combinations/combineWithRepetitions.js
+++ b/src/algorithms/sets/combinations/combineWithRepetitions.js
@@ -4,6 +4,8 @@
  * @return {*[]}
  */
 export default function combineWithRepetitions(comboOptions, comboLength) {
+  // If the length of the combination is 1 then each element of the original array
+  // is a combination itself.
   if (comboLength === 1) {
     return comboOptions.map(comboOption => [comboOption]);
   }
@@ -11,14 +13,16 @@ export default function combineWithRepetitions(comboOptions, comboLength) {
   // Init combinations array.
   const combos = [];
 
-  // Eliminate characters one by one and concatenate them to
-  // combinations of smaller lengths.
+  // Remember characters one by one and concatenate them to combinations of smaller lengths.
+  // We don't extract elements here because the repetitions are allowed.
   comboOptions.forEach((currentOption, optionIndex) => {
+    // Generate combinations of smaller size.
     const smallerCombos = combineWithRepetitions(
       comboOptions.slice(optionIndex),
       comboLength - 1,
     );
 
+    // Concatenate currentOption with all combinations of smaller size.
     smallerCombos.forEach((smallerCombo) => {
       combos.push([currentOption].concat(smallerCombo));
     });
diff --git a/src/algorithms/sets/combinations/combineWithoutRepetitions.js b/src/algorithms/sets/combinations/combineWithoutRepetitions.js
index 56c1e8fe..ef08b8b6 100644
--- a/src/algorithms/sets/combinations/combineWithoutRepetitions.js
+++ b/src/algorithms/sets/combinations/combineWithoutRepetitions.js
@@ -4,6 +4,8 @@
  * @return {*[]}
  */
 export default function combineWithoutRepetitions(comboOptions, comboLength) {
+  // If the length of the combination is 1 then each element of the original array
+  // is a combination itself.
   if (comboLength === 1) {
     return comboOptions.map(comboOption => [comboOption]);
   }
@@ -11,14 +13,16 @@ export default function combineWithoutRepetitions(comboOptions, comboLength) {
   // Init combinations array.
   const combos = [];
 
-  // Eliminate characters one by one and concatenate them to
-  // combinations of smaller lengths.
+  // Extract characters one by one and concatenate them to combinations of smaller lengths.
+  // We need to extract them because we don't want to have repetitions after concatenation.
   comboOptions.forEach((currentOption, optionIndex) => {
+    // Generate combinations of smaller size.
     const smallerCombos = combineWithoutRepetitions(
       comboOptions.slice(optionIndex + 1),
       comboLength - 1,
     );
 
+    // Concatenate currentOption with all combinations of smaller size.
     smallerCombos.forEach((smallerCombo) => {
       combos.push([currentOption].concat(smallerCombo));
     });