Example: Maximum Scalar Product in C

// Maximum Scalar Product
#include <stdio.h>
#include <stdlib.h> // Required for qsort

// Comparison function for qsort (ascending order)
int compareIntegers(const void *a, const void *b) {
    return (*(int*)a - *(int*)b);
}

// Function to calculate maximum scalar product
long long maxScalarProduct(int arr1[], int arr2[], int n) {
    // Step 1: Sort both arrays in ascending order
    qsort(arr1, n, sizeof(int), compareIntegers);
    qsort(arr2, n, sizeof(int), compareIntegers);

    // Step 2: Calculate the scalar product
    long long product = 0;
    for (int i = 0; i < n; i++) {
        product += (long long)arr1[i] * arr2[i];
    }
    return product;
}

int main() {
    // Step 1: Define input vectors and their size
    int arr1[] = {1, 2, 3};
    int arr2[] = {4, 5, 6};
    int n1 = sizeof(arr1) / sizeof(arr1[0]);
    int n2 = sizeof(arr2) / sizeof(arr2[0]);

    if (n1 != n2) {
        printf("Error: Vectors must have the same dimension.\n");
        return 1;
    }

    // Step 2: Calculate and print the maximum scalar product
    long long result = maxScalarProduct(arr1, arr2, n1);
    printf("The maximum scalar product is: %lld\n", result);
    
    // Another example
    int arr3[] = { -1, -2, -3 };
    int arr4[] = { 1, 2, 3 };
    int n3 = sizeof(arr3) / sizeof(arr3[0]);
    
    result = maxScalarProduct(arr3, arr4, n3);
    printf("The maximum scalar product for {-1, -2, -3} and {1, 2, 3} is: %lld\n", result);

    return 0;
}