diff --git a/src/algorithms/sorting/merge-sort/MergeSort.js b/src/algorithms/sorting/merge-sort/MergeSort.js index 6a2f8a84..b6eb73f0 100644 --- a/src/algorithms/sorting/merge-sort/MergeSort.js +++ b/src/algorithms/sorting/merge-sort/MergeSort.js @@ -1,4 +1,4 @@ -import Sort from '../Sort'; +import Sort from "../Sort"; export default class MergeSort extends Sort { sort(originalArray) { @@ -24,36 +24,42 @@ export default class MergeSort extends Sort { } mergeSortedArrays(leftArray, rightArray) { - let sortedArray = []; + const sortedArray = []; - // In case if arrays are not of size 1. - while (leftArray.length && rightArray.length) { - let minimumElement = null; + // Use array pointers to exclude old elements after they have been added to the sorted array + let leftIndex = 0; + let rightIndex = 0; - // Find minimum element of two arrays. - if (this.comparator.lessThanOrEqual(leftArray[0], rightArray[0])) { - minimumElement = leftArray.shift(); + while (leftIndex < leftArray.length && rightIndex < rightArray.length) { + // Find the minimum element between the left and right array + if ( + this.comparator.lessThanOrEqual( + leftArray[leftIndex], + rightArray[rightIndex] + ) + ) { + sortedArray.push(leftArray[leftIndex]); + + // Increment index pointer to the right + leftIndex += 1; + + // Call visiting callback. + this.callbacks.visitingCallback(leftArray[leftIndex]); } else { - minimumElement = rightArray.shift(); + sortedArray.push(rightArray[rightIndex]); + + // Increment index pointer to the right + rightIndex += 1; + + // Call visiting callback. + this.callbacks.visitingCallback(rightArray[rightIndex]); } - - // Call visiting callback. - this.callbacks.visitingCallback(minimumElement); - - // Push the minimum element of two arrays to the sorted array. - sortedArray.push(minimumElement); } - // If one of two array still have elements we need to just concatenate - // this element to the sorted array since it is already sorted. - if (leftArray.length) { - sortedArray = sortedArray.concat(leftArray); - } - - if (rightArray.length) { - sortedArray = sortedArray.concat(rightArray); - } - - return sortedArray; + // There will be one element remaining from either the left OR the right + // Concatenate the remaining element into the sorted array + return sortedArray + .concat(leftArray.slice(leftIndex)) + .concat(rightArray.slice(rightIndex)); } }