Quick Sort

1. Select an element from the sequence, referred to as the "pivot";
2. Rearrange the sequence so that all elements smaller than the pivot value are placed before it, and all elements larger than the pivot value are placed after it (equal elements can be placed on either side). After this partitioning step, the pivot is positioned in the middle of the sequence. This operation is called partitioning;
3. Recursively sort the sub-sequences consisting of elements smaller than the pivot value and elements larger than the pivot value;

Code Implementation

::: code-tabs
@tab Java

public class QuickSort implements IArraySort {
    @Override
    public int[] sort(int[] sourceArray) throws Exception {
        // Create a copy of arr to avoid modifying the original parameter content
        int[] arr = Arrays.copyOf(sourceArray, sourceArray.length);
        return quickSort(arr, 0, arr.length - 1);
    }
    private int[] quickSort(int[] arr, int left, int right) {
        if (left < right) {
            int partitionIndex = partition(arr, left, right);
            quickSort(arr, left, partitionIndex - 1);
            quickSort(arr, partitionIndex + 1, right);
        }
        return arr;
    }
    private int partition(int[] arr, int left, int right) {
        // Set the pivot value
        int pivot = left;
        int index = pivot + 1;
        for (int i = index; i <= right; i++) {
            if (arr[i] < arr[pivot]) {
                swap(arr, i, index);
                index++;
            }
        }
        swap(arr, pivot, index - 1);
        return index - 1;
    }
    private void swap(int[] arr, int i, int j) {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

@tab JavaScript

function quickSort(arr, left, right) {
    var len = arr.length,
        partitionIndex,
        left = typeof left != 'number' ? 0 : left,
        right = typeof right != 'number' ? len - 1 : right;
    if (left < right) {
        partitionIndex = partition(arr, left, right);
        quickSort(arr, left, partitionIndex-1);
        quickSort(arr, partitionIndex+1, right);
    }
    return arr;
}
function partition(arr, left ,right) {     // Partition operation
    var pivot = left,                      // Set the pivot value
        index = pivot + 1;
    for (var i = index; i <= right; i++) {
        if (arr[i] < arr[pivot]) {
            swap(arr, i, index);
            index++;
        }        
    }
    swap(arr, pivot, index - 1);
    return index-1;
}
function swap(arr, i, j) {
    var temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}
function partition2(arr, low, high) {
  let pivot = arr[low];
  while (low < high) {
    while (low < high && arr[high] > pivot) {
      --high;
    }
    arr[low] = arr[high];
    while (low < high && arr[low] <= pivot) {
      ++low;
    }
    arr[high] = arr[low];
  }
  arr[low] = pivot;
  return low;
}
function quickSort2(arr, low, high) {
  if (low < high) {
    let pivot = partition2(arr, low, high);
    quickSort2(arr, low, pivot - 1);
    quickSort2(arr, pivot + 1, high);
  }
  return arr;
}

@tab Python

def quickSort(arr, left=None, right=None):
    left = 0 if not isinstance(left,(int, float)) else left
    right = len(arr)-1 if not isinstance(right,(int, float)) else right
    if left < right:
        partitionIndex = partition(arr, left, right)
        quickSort(arr, left, partitionIndex-1)
        quickSort(arr, partitionIndex+1, right)
    return arr
def partition(arr, left, right):
    pivot = left
    index = pivot+1
    i = index
    while  i <= right:
        if arr[i] < arr[pivot]:
            swap(arr, i, index)
            index+=1
        i+=1
    swap(arr,pivot,index-1)
    return index-1
def swap(arr, i, j):
    arr[i], arr[j] = arr[j], arr[i]

@tab Go

func quickSort(arr []int) []int {
    return _quickSort(arr, 0, len(arr)-1)
}
func _quickSort(arr []int, left, right int) []int {
    if left < right {
        partitionIndex := partition(arr, left, right)
        _quickSort(arr, left, partitionIndex-1)
        _quickSort(arr, partitionIndex+1, right)
    }
    return arr
}
func partition(arr []int, left, right int) int {
    pivot := left
    index := pivot + 1
    for i := index; i <= right; i++ {
        if arr[i] < arr[pivot] {
            swap(arr, i, index)
            index += 1
        }
    }
    swap(arr, pivot, index-1)
    return index - 1
}
func swap(arr []int, i, j int) {
    arr[i], arr[j] = arr[j], arr[i]
}

@tab PHP

function quickSort($arr)
{
    if (count($arr) <= 1)
        return $arr;
    $middle = $arr[0];
    $leftArray = array();
    $rightArray = array();
    for ($i = 1; $i < count($arr); $i++) {
        if ($arr[$i] > $middle)
            $rightArray[] = $arr[$i];
        else
            $leftArray[] = $arr[$i];
    }
    $leftArray = quickSort($leftArray);
    $leftArray[] = $middle;
    $rightArray = quickSort($rightArray);
    return array_merge($leftArray, $rightArray);
}

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