Encryption.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();

/*
 * Complete the 'encryption' function below.
 *
 * The function is expected to return a STRING.
 * The function accepts STRING s as parameter.
 */

/*
 * To return the string from the function, you should either do static allocation or dynamic allocation
 *
 * For example,
 * char* return_string_using_static_allocation() {
 *     static char s[] = "static allocation of string";
 *
 *     return s;
 * }
 *
 * char* return_string_using_dynamic_allocation() {
 *     char* s = malloc(100 * sizeof(char));
 *
 *     s = "dynamic allocation of string";
 *
 *     return s;
 * }
 *
 */
char* encryption(char* s) {
    int messageLength = strlen(s);
    int column = 0, row = 0;
    int sq = sqrt(messageLength);
    if (sq * sq == messageLength) {
        column = row = sq;
    } else {
        row = sq;
        column = sq + 1;
        if (row * column < messageLength) {
            row = sq + 1;
            column = sq + 1;
        }
    }
    char *result = (char *)calloc(messageLength + column, sizeof(char));
    int p = 0;
    for (int j = 0; j < column; ++j)
    {
        for (int k = 0; k < row; ++k)
        {
            if (j + k * column < messageLength) {
                result[p] = s[j + k * column];
                p++;
            }
        }
        result[p] = ' ';
        p++;
    }
    return result;
}

int main()
{
    FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w");
    char* s = readline();
    char* result = encryption(s);
    fprintf(fptr, "%s\n", result);
    fclose(fptr);
    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;
}