Fix btPowerSet() comments.

Author: trekhleb

src/algorithms/sets/power-set/btPowerSet.js

@@ -6,16 +6,23 @@
  * @return {*[][]} - All subsets of original set.
  */
 function btPowerSetRecursive(originalSet, allSubsets = [[]], currentSubSet = [], startAt = 0) {
-  // In order to avoid duplication we need to start from next element every time we're forming a
-  // subset. If we will start from zero then we'll have duplicates like {3, 3, 3}.
+  // Let's iterate over originalSet elements that may be added to the subset
+  // without having duplicates. The value of startAt prevents adding the duplicates.
   for (let position = startAt; position < originalSet.length; position += 1) {
-    // Let's push current element to the subset.
+    // Let's push current element to the subset
     currentSubSet.push(originalSet[position]);
+
     // Current subset is already valid so let's memorize it.
+    // We do array destruction here to save the clone of the currentSubSet.
+    // We need to save a clone since the original currentSubSet is going to be
+    // mutated in further recursive calls.
     allSubsets.push([...currentSubSet]);
-    // Let's try to form all other subsets for the current subset.
+
+    // Let's try to generate all other subsets for the current subset.
+    // We're increasing the position by one to avoid duplicates in subset.
     btPowerSetRecursive(originalSet, allSubsets, currentSubSet, position + 1);
-    // BACKTRACK. Exclude last element from the subset and try the next one.
+
+    // BACKTRACK. Exclude last element from the subset and try the next valid one.
     currentSubSet.pop();
   }