ExtraLongFactorials.c

#include <assert.h>
#include <ctype.h>
#include <limits.h>
#include <math.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* readline();
char* ltrim(char*);
char* rtrim(char*);

int parse_int(char*);

/*
 * Complete the 'extraLongFactorials' function below.
 *
 * The function accepts INTEGER n as parameter.
 */

void extraLongFactorials(int n) {
    // Array to store large numbers as digits
    int result[1000];
    result[0] = 1; // Initialize with 1
    int result_size = 1;

    // Multiply numbers from 2 to n
    for (int x = 2; x <= n; x++) {
        int carry = 0;

        // Multiply x with the current result
        for (int i = 0; i < result_size; i++) {
            int prod = result[i] * x + carry;
            result[i] = prod % 10; // Store last digit in the array
            carry = prod / 10;    // Get the carry
        }

        // Store remaining carry in result array
        while (carry) {
            result[result_size] = carry % 10;
            carry /= 10;
            result_size++;
        }
    }

    // Print the result in reverse (since the most significant digit is at the end)
    for (int i = result_size - 1; i >= 0; i--) {
        printf("%d", result[i]);
    }
    printf("\n");
}

int main()
{
    int n = parse_int(ltrim(rtrim(readline())));

    extraLongFactorials(n);

    return 0;
}

char* readline() {
    size_t alloc_length = 1024;
    size_t data_length = 0;

    char* data = malloc(alloc_length);

    while (true) {
        char* cursor = data + data_length;
        char* line = fgets(cursor, alloc_length - data_length, stdin);

        if (!line) {
            break;
        }

        data_length += strlen(cursor);

        if (data_length < alloc_length - 1 || data[data_length - 1] == '\n') {
            break;
        }

        alloc_length <<= 1;

        data = realloc(data, alloc_length);

        if (!data) {
            data = '\0';

            break;
        }
    }

    if (data[data_length - 1] == '\n') {
        data[data_length - 1] = '\0';

        data = realloc(data, data_length);

        if (!data) {
            data = '\0';
        }
    } else {
        data = realloc(data, data_length + 1);

        if (!data) {
            data = '\0';
        } else {
            data[data_length] = '\0';
        }
    }

    return data;
}

char* ltrim(char* str) {
    if (!str) {
        return '\0';
    }

    if (!*str) {
        return str;
    }

    while (*str != '\0' && isspace(*str)) {
        str++;
    }

    return str;
}

char* rtrim(char* str) {
    if (!str) {
        return '\0';
    }

    if (!*str) {
        return str;
    }

    char* end = str + strlen(str) - 1;

    while (end >= str && isspace(*end)) {
        end--;
    }

    *(end + 1) = '\0';

    return str;
}

int parse_int(char* str) {
    char* endptr;
    int value = strtol(str, &endptr, 10);

    if (endptr == str || *endptr != '\0') {
        exit(EXIT_FAILURE);
    }

    return value;
}