chore: merge add QuickSortRecursive method. (TheAlgorithms#690)

suryapratapsinghsuryavanshi · web-flow · commit 77a2411395e5 · 2021-09-19T18:55:25.000+05:30
* add QuickSortRecursive method

* added an exception for test cases

* fix for test cases

* added test cases for QuickSortRecursive
diff --git a/Sorts/QuickSortRecursive.js b/Sorts/QuickSortRecursive.js
@@ -0,0 +1,59 @@
+/*
+    Quicksort is the most popular sorting algorithm and there have
+    lots of different implementations but the "recursive" or "Partition in place"
+    is one of the most efficient implementations below we have discussed how to
+    implement it.
+
+    Partition in place => "in place" Partition in place indicates that we
+    do not need any other space to store the auxiliary array and the term
+    "partition" denotes that we split the list into two parts one is less
+    than the pivot and the other is greater than the pivot and repeats this
+    process recursively and breaks the problem into sub-problems and makes
+    it singular so that the behavior or "divide and conquer" get involved
+    too.
+
+    Problem & Source of Explanation => https://www.cs.auckland.ac.nz/software/AlgAnim/qsort1a.html
+*/
+
+/**
+ * Partition in place QuickSort.
+ * @param {number[]} inputList list of values.
+ * @param {number} low lower index for partition.
+ * @param {number} high higher index for partition.
+ */
+const quickSort = (inputList, low, high) => {
+  if (!Array.isArray(inputList)) {
+    throw new TypeError('Please input a valid list or array.')
+  }
+  if (low < high) {
+    // get the partition index.
+    const pIndex = partition(inputList, low, high)
+    // recursively call the quickSort method again.
+    quickSort(inputList, low, pIndex - 1)
+    quickSort(inputList, pIndex + 1, high)
+  }
+  return inputList
+}
+
+/**
+ * Partition In Place method.
+ * @param {number[]} partitionList list for partiting.
+ * @param {number} low lower index for partition.
+ * @param {number} high higher index for partition.
+ * @returns {number} `pIndex` pivot index value.
+ */
+const partition = (partitionList, low, high) => {
+  const pivot = partitionList[high]
+  let pIndex = low
+  for (let index = low; index <= high - 1; index++) {
+    if (partitionList[index] < pivot) {
+      // swap variables using array destructuring
+      [partitionList[index], partitionList[pIndex]] = [partitionList[pIndex], partitionList[index]]
+      pIndex += 1
+    }
+  }
+  [partitionList[pIndex], partitionList[high]] = [partitionList[high], partitionList[pIndex]]
+  return pIndex
+}
+
+export { quickSort }
diff --git a/Sorts/QuickSortRecursive.test.js b/Sorts/QuickSortRecursive.test.js
@@ -0,0 +1,21 @@
+import { quickSort } from './QuickSortRecursive'
+
+describe('QuickSortRecursive | Partition In Place Method', () => {
+  it('Expectedly, throw some error if we pass a non-array input', () => {
+    expect(() => quickSort('xyz', 0, 2)).toThrow('Please input a valid list or array.')
+    expect(() => quickSort(null, 0, 4)).toThrow('Please input a valid list or array.')
+    expect(() => quickSort(55, 0, 2)).toThrow('Please input a valid list or array.')
+  })
+
+  it('Expectedly, the quickSort method will sort the unsorted list in ascending order', () => {
+    const unSortArray = [5, 9, 3, 4, 6, 2, 0, 1, 7, 8]
+    const sortedExpectedArray = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+    expect(quickSort(unSortArray, 0, unSortArray.length - 1)).toEqual(sortedExpectedArray)
+  })
+
+  it('Expectedly, the quickSort method will arrange the list of character values in dictionary order.', () => {
+    const unSortList = ['d', 'e', 'c', 'a', 'f', 'b']
+    const sortedExpectedList = ['a', 'b', 'c', 'd', 'e', 'f']
+    expect(quickSort(unSortList, 0, unSortList.length - 1)).toEqual(sortedExpectedList)
+  })
+})
