How Quick Sort Works in Data Structure?


Larry Thompson

Quick Sort is a popular sorting algorithm used in data structures. It follows the divide-and-conquer approach, where it recursively divides the array into smaller subarrays and sorts them individually. The algorithm’s efficiency is based on its ability to efficiently partition the array and its average-case time complexity of O(n log n).

How Quick Sort Works:

The Quick Sort algorithm works by selecting a pivot element from the array, partitioning the other elements into two subarrays according to whether they are less than or greater than the pivot, and then recursively sorting those subarrays.

To understand how Quick Sort works, let’s go through the steps involved:

Step 1: Choosing a Pivot:

The first step of Quick Sort is to choose a pivot element. The pivot can be any element from the array. In most cases, it is common to choose either the first or last element as the pivot.

Step 2: Partitioning:

In this step, we rearrange the array so that all elements smaller than the pivot come before it, and all elements greater than it come after. This process is known as partitioning.

  • Pivot Selection: Suppose we choose the last element as our pivot.
  • Partitioning Algorithm: We maintain two pointers – i and j. Pointer i starts at -1 and keeps track of the position where we should place elements smaller than or equal to the pivot. Pointer j traverses through each element of the array.

We compare each element with the chosen pivot. If an element is smaller than or equal to the pivot, we swap it with arr[i].

After every swap operation, we increment i by one. At the end of this process, all elements smaller than or equal to the pivot will be on the left side of i.

Step 3: Recursion:

After partitioning the array, we have two subarrays – one with elements smaller than the pivot and one with elements greater than the pivot. We recursively apply the above steps to these subarrays until they become sorted.

By dividing the array into smaller subarrays and sorting them individually, Quick Sort efficiently reduces the sorting problem’s size. This divide-and-conquer approach helps Quick Sort achieve its average-case time complexity of O(n log n).

Advantages of Quick Sort:

  • Efficiency: Quick Sort is one of the fastest sorting algorithms in practice.
  • In-place Sorting: Quick Sort requires only a small amount of additional memory space, making it an in-place sorting algorithm.
  • Widely Used: Quick Sort is widely used due to its efficiency and ease of implementation.


In summary, Quick Sort is a popular sorting algorithm that follows the divide-and-conquer approach. By efficiently partitioning and recursively sorting subarrays, it achieves an average-case time complexity of O(n log n). Its efficiency, in-place nature, and widespread usage make it a preferred choice for sorting large datasets.

I hope this article has provided you with a clear understanding of how Quick Sort works in data structures!

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