c++ quicksort

A quicksort algorithm in C++ follows these steps:

  1. Choose a pivot element from the array. This element will be used to divide the array into two smaller sub-arrays.
  2. Partition the array into two sub-arrays: one containing elements smaller than the pivot, and the other containing elements greater than the pivot.
  3. Recursively apply the quicksort algorithm to each of the sub-arrays created in the previous step.
  4. Combine the sorted sub-arrays to get the final sorted array.

Here is a step-by-step explanation of the quicksort algorithm:

Step 1: Choose a pivot element from the array. This can be any element from the array, but it is often chosen as the last element.

Step 2: Partition the array into two sub-arrays. To do this, we maintain two pointers: 'low' and 'high'. The 'low' pointer starts at the beginning of the array, and the 'high' pointer starts at the end of the array. The goal is to move elements smaller than the pivot to the left side of the array, and elements greater than the pivot to the right side of the array.

  • Initialize 'low' and 'high' pointers to the first and last indices of the array, respectively.
  • While 'low' is less than or equal to 'high', repeat the following steps:
    • Increment 'low' until an element greater than the pivot is found.
    • Decrement 'high' until an element smaller than the pivot is found.
    • If 'low' is still less than or equal to 'high', swap the elements at 'low' and 'high'.
  • Once 'low' is greater than 'high', swap the pivot element (which is currently at the last index) with the element at 'low'.

Step 3: Recursively apply the quicksort algorithm to each of the sub-arrays created in the previous step. This is done by calling the quicksort function on the left sub-array (from the beginning of the array to the pivot index - 1) and the right sub-array (from the pivot index + 1 to the end of the array).

Step 4: Combine the sorted sub-arrays to get the final sorted array. Since the sub-arrays are sorted in place, no extra merging step is required.

This process is repeated recursively until the entire array is sorted. The pivot element is chosen in such a way that it guarantees progress towards a sorted array with each recursive call.