quickSort.js

quickSort.js

const quickSort = (targetArray, lowIndex, highIndex) => {

  const swap = (targetArray, lowIndex, highIndex) => {
    let temp = targetArray[lowIndex]
    targetArray[lowIndex] = targetArray[highIndex]
    targetArray[highIndex] = temp
  }

  //pivotElement will be the value of the element closest to the middle of the array
  let pivotElement = targetArray[Math.floor((highIndex + lowIndex) / 2)]//middle element
  
  //at the start, set leftPointer to lowIndex
  let leftPointer = lowIndex
  
  //at the start, st rightPointer to highIndex
  let rightPointer = highIndex
  
  //the outer while loop contines until the pointers converge and are equal
  while (leftPointer <= rightPointer) {
    
    while (targetArray[leftPointer] < pivotElement) {
      leftPointer++
    }
    
    while (targetArray[rightPointer] > pivotElement) {
      rightPointer--
    }

    if (leftPointer <= rightPointer) {
      swap(targetArray, leftPointer, rightPointer) //swap two elements
      leftPointer++
      rightPointer--
    }
  
  }

  //more elements on the left side of the pivot
  if (lowIndex < leftPointer - 1) { 
    quickSort(targetArray, lowIndex, leftPointer - 1)
  }
  
  //more elements on the right side of the pivot
  if (leftPointer < highIndex) { 
    quickSort(targetArray, leftPointer, highIndex)
  }

  return targetArray
}

//the array to sort
const unsortedArray = [7, 0, 2, 1, 9, 2]
console.log('unsortedArray', unsortedArray)

//set a lowIndex for the index of the first element
const lowIndex = 0

//set highIndex, for the index of the last element
const highIndex = unsortedArray.length - 1
//we have to set these as variables, because quicksort is a recursive function

//pass in the unsorted array, lowIndex and highIndex to quickSort function
const sorted = quickSort(unsortedArray, lowIndex, highIndex)

//display sorted array
console.log('sorted', sorted)