QuickSort Notes - GoMani/algorithms GitHub Wiki

First step:

  Choose pivot 

• Simple rule : choose the index high as pivot
• Partition by pivot

  // start and end are index postion
 partition(int[] arr, int start,int end){
       // Set i the position where the smallest element last inserted or
       //  we can point to position where we want to insert the next small element
       int i=start-1; 
       int pivot=arr[end];
       for(int j=start;j < end;j++){
           if(arr[j] <= pivot) { 
               
             i++;
             swap(arr[j],arr[i]);
            }
       }
       // Step 2 bring the pivot to the right position
       swap(arr[end],arr[i+1]);
      // return pivot index
     return i+1;
}

• based on pivot partition the array

 quickSort(int[] array, int start, int end) {
   if(start < end) {
   int pivotIndex= partition(array,start,end);
    quickSort(array,start,pivotIndex-1);
    quickSort(array,pivotIndex+1,end);
  }
 
}