Quick Sort

class Solution
{
      static void swap(int[] arr, int x, int y)
      {
        int temp = arr[x];
        arr[x] = arr[y];
        arr[y] = temp;
    }
    
    //Function to sort an array using quick sort algorithm.
    static void quickSort(int arr[], int st, int end)
    {
        if(st >= end) return;
        int pi = partition(arr, st, end);
        quickSort(arr, st, pi-1);
        quickSort(arr, pi+1, end);
        }
        
        static int partition(int arr[], int st, int end)
    {
       int pivot = arr[st];
        int cnt = 0;
        for(int i = st+1; i <= end; i++)
        {
            if(arr[i] <= pivot) cnt++;
        }
        
        int pivotIdx = st + cnt;
        swap(arr, st, pivotIdx);
        int i = st, j = end;
       
        while(i < pivotIdx && j > pivotIdx)
        {
            while (arr[i] <= pivot) i++;
            while (arr[j] > pivot) j--;
            if(i < pivotIdx && j > pivotIdx)
            {
                swap(arr, i, j);
                i++;
                j--;
            }
        }
        return pivotIdx;
        
    } 
}