Quicksort & Mergesort With C

#include <stdio.h>

// Function to swap two elements
void swap(int* a, int* b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

// Function to partition array for quicksort
int partition(int arr[], int low, int high) {
    int pivot = arr[high];
    int i = low - 1;

    for (int j = low; j <= high - 1; j++) {
        if (arr[j] < pivot) {
            i++;
            swap(&arr[i], &arr[j]);
        }
    }

    swap(&arr[i + 1], &arr[high]);
    return i + 1;
}

// Quicksort algorithm
void quicksort(int arr[], int low, int high) {
    if (low < high) {
        int pi = partition(arr, low, high);

        quicksort(arr, low, pi - 1);
        quicksort(arr, pi + 1, high);
    }
}

// Function to merge two subarrays for mergesort
void merge(int arr[], int left, int mid, int right) {
    int n1 = mid - left + 1;
    int n2 = right - mid;

    int leftArr[n1];
    int rightArr[n2];

    for (int i = 0; i < n1; i++) {
        leftArr[i] = arr[left + i];
    }
    for (int j = 0; j < n2; j++) {
        rightArr[j] = arr[mid + 1 + j];
    }

    int i = 0, j = 0, k = left;

    while (i < n1 && j < n2) {
        if (leftArr[i] <= rightArr[j]) {
            arr[k] = leftArr[i];
            i++;
        } else {
            arr[k] = rightArr[j];
            j++;
        }
        k++;
    }

    while (i < n1) {
        arr[k] = leftArr[i];
        i++;
        k++;
    }

    while (j < n2) {
        arr[k] = rightArr[j];
        j++;
        k++;
    }
}

// Mergesort algorithm
void mergesort(int arr[], int left, int right) {
    if (left < right) {
        int mid = (left + right) / 2;

        mergesort(arr, left, mid);
        mergesort(arr, mid + 1, right);

        merge(arr, left, mid, right) ;
    }
}

// Function to print an array
void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int arr1[] = {10, 7, 8, 9, 1, 5};
    int n1 = sizeof(arr1) / sizeof(arr1[0]);

    printf("Original array: ");
    printArray(arr1, n1);

    quicksort(arr1, 0, n1 - 1);
    printf("Array after QuickSort: ");
    printArray(arr1, n1);

    int arr2[] = {10, 7, 8, 9, 1, 5};
    int n2 = sizeof(arr2) / sizeof(arr2[0]);

    printf("Original array: ");
    printArray(arr2, n2);

    mergesort(arr2, 0, n2 - 1);
    printf("Array after MergeSort: ");
    printArray(arr2, n2);

    return 0;
}

Comments

[Bill C]

which of these implementations are stable? ie if the value at i and j in the array have the same sort value, with i<j, do those values end up at places i' and j' where i'<j'?

Also, title says C, tags say java, which is it?