Implementing Quicksort to Visualize Each Partition

When implementing the quicksort algorithm, ensuring that you visualize the array after each partition can significantly aid in understanding the sorting process. In this article, we will introduce how to modify the quicksort function to print the array after every partition step. This is a great way to monitor the sorting progress, especially for educational or debugging purposes. We will also provide the C code for this modified quicksort implementation.

Overview of Quicksort

Quicksort is a divide-and-conquer sorting algorithm. The algorithm picks an element as a pivot and partitions the given array around the picked pivot. The pivot selection can vary, but a common approach is to choose the last element as the pivot. The array is partitioned in such a way that all elements smaller than the pivot come before it, and all elements greater than the pivot come after it.

Modifying the Quicksort Algorithm to Print After Each Partition

To visualize the array after each partition, we need to add specific print statements at the appropriate points in the quicksort function. We will also define a partition function to encapsulate the logic of partitioning the array.

The Code Implementation

#include stdio.h
int n;
// Function to swap two integers
void swap(int *a, int *b) {
    int temp  *a;
    *a  *b;
    *b  temp;
}
// Function to partition the array and return the pivot index
int partition(int a[], int start, int end) {
    int pivotIndex  start, x  a[end];
    int i;
    for (i  start; i  end; i  ) {
        if (a[i]  x) {
            swap(a[i], a[pivotIndex]);
            pivotIndex  ;
        }
    }
    swap(a[pivotIndex], a[end]);
    // Print the array after each partition
    for (int i  start; i  end; i  ) {
        printf(%d , a[i]);
    }
    printf(
);
    return pivotIndex;
}
// Recursive quicksort function
void quicksort(int a[], int start, int end) {
    if (start  end) {
        int pIndex  partition(a, start, end);
        quicksort(a, start, pIndex - 1);
        quicksort(a, pIndex   1, end);
    }
}
int main() {
    scanf(%d, n);
    int a[n];
    for (int i  0; i  n; i  ) {
        scanf(%d, a[i]);
    }
    quicksort(a, 0, n - 1);
    int start  0, end  n - 1;
    for (int i  start; i  end; i  ) {
        printf(%d , a[i]);
    }
    printf(
);
    return 0;
}

Explanation

Function swap: This function takes two integers by reference and swaps their values. Function partition: This function takes an array and two indices as input, performs the partitioning, and returns the index of the pivot element. After partitioning, it prints the array to visualize the current state. Function quicksort: This function recursively partitions the array and sorts the sub-arrays. Function main: This function reads the array from input, calls the quicksort function, and prints the sorted array.

Conclusion

Implementing the quicksort algorithm to print the array after each partition is a simple yet effective way to visualize the sorting process. This can be particularly useful for educational purposes, debugging, or simply understanding how the quicksort algorithm works. The provided code demonstrates this modification and can be used as a basis for further experimentation or real-world applications.

Keywords

quicksort partition visualization C programming printing array