char* kth_word_in_mth_sentence_of_nth_paragraph(char**** document, int k, int m, int n) {
    return document[n-1][m-1][k-1];
}

char** kth_sentence_in_mth_paragraph(char**** document, int k, int m) {
    return document[m-1][k-1];
}

char*** kth_paragraph(char**** document, int k) {
    return document[k-1];
}

char** split_string(char* text, char delim) {
    assert(text != NULL);
    char** result = malloc(1*sizeof(char*));
    int size = 1;
    
    char* temp = strtok(text, &delim);
    *result = temp;
    
    while(temp != NULL) {
        size++;
        result = realloc(result,size*sizeof(char*));
        temp = strtok(NULL, &delim);
        result[size-1] = temp;
    }
    return result;
}

char**** get_document(char* text) {
    assert(text != NULL);
    
    // split text by '\n' and count number of paragraphs
    char** paragraphs = split_string(text, '\n');
    int npar = 0;
    while (paragraphs[npar] != NULL) {
        npar++;
    }
    
    char**** doc = malloc((npar+1)*sizeof(char***));
    // set last position to NULL for the user
    // to know when the array ends.
    doc[npar] = NULL; 
    
    int i = 0;
    while (paragraphs[i] != NULL) {
        
        // split sentences of paragraph by '.' and count number of sentences
        char** sentences = split_string(paragraphs[i], '.');
        int nsen = 0;
        while(sentences[nsen] != NULL) {
            nsen++;
        }
        
        doc[i] = malloc((nsen+1)*sizeof(char**));
        // set last position to NULL for the user
        // to know when the array ends.
        doc[i][nsen] = NULL; 
        
        int j = 0;
        while (sentences[j] != NULL) {
            
            // remember that doc[0][0] means: paragraph #0,
            // sentence #0 and should act like a pointer to
            // the first element of an array of words (strings)
            
            // split string by ' ' and associate doc[i][j]
            // with the array of strings representing words
            // that is returned by split_string.
            doc[i][j] = split_string(sentences[j], ' ');
            j++;
        }
        i++;
    }
    
    return doc; 
}