Quick Sort as Divide and Conquer in DSA C - Build from Scratch

Quick Sort as Divide and Conquer

📖 Scenario: You are working on a program that sorts a list of numbers quickly. Sorting helps organize data so you can find things faster, like arranging books by title on a shelf.

🎯 Goal: Build a program that uses the Quick Sort method to sort an array of integers in ascending order. Quick Sort works by dividing the list into smaller parts, sorting those parts, and then combining them.

📋 What You'll Learn

Create an integer array with exact values

Define a pivot index variable

Implement the partition function to divide the array

Implement the quickSort function using divide and conquer

Print the sorted array in the final step

💡 Why This Matters

🌍 Real World

Quick Sort is used in many software systems to organize data quickly, such as sorting search results or arranging files.

💼 Career

Understanding Quick Sort helps in coding interviews and building efficient programs that handle large data sets.

1

Create the integer array

Create an integer array called arr with these exact values: 29, 10, 14, 37, 13 and an integer n set to the size of arr.

DSA C

int arr[] = {29, 10, 14, 37, 13};
int n = sizeof(arr) / sizeof(arr[0]);
// Your code here

Hint

Use sizeof(arr) / sizeof(arr[0]) to get the number of elements in the array.

2

Define the pivot index and partition function

Define an integer variable pivot inside the partition function. Write the partition function that takes the array arr, low, and high indexes, uses the last element as pivot, and partitions the array so that elements less than pivot come before it and greater come after.

DSA C

int partition(int arr[], int low, int high) {
    int pivot = arr[high];
    int i = (low - 1);
    // Your code here
}

Hint

The pivot is the last element arr[high]. Use a loop from low to high - 1 to compare elements with pivot.

3

Implement the quickSort function

Write the quickSort function that takes the array arr, low, and high indexes. Use divide and conquer by calling partition to get the pivot index, then recursively call quickSort on the left and right parts of the array.

DSA C

void quickSort(int arr[], int low, int high) {
    if (low < high) {
        int pi = partition(arr, low, high);
        // Your code here
    }
}

Hint

Use recursion to sort the parts before and after the pivot index returned by partition.

4

Print the sorted array

Call quickSort with arr, 0, and n - 1. Then print the sorted array elements separated by spaces on one line.

DSA C

int main() {
    quickSort(arr, 0, n - 1);
    // Print the sorted array
    // Your code here
    return 0;
}

Hint

Call quickSort(arr, 0, n - 1) and then use a for loop to print each element with printf.