usaa20/cv5/a_train.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "a_train.h"


struct car *add_car(struct car *first, const char *target)
{
    struct car *curr_car = (struct car*) calloc(1, sizeof(struct car));
    strcpy(curr_car -> value, target);
    curr_car -> next = NULL;
    if (first == NULL)
    {
        // create list if necessary
        return curr_car;
    }
    // add car to the end
    struct car *prev_car = first;
    while (prev_car -> next != NULL)
    {
        prev_car = prev_car -> next;
    }
    prev_car -> next = curr_car;
    return first;
}


void print_train(struct car *first)
{
    struct car *curr_car = first;
    while (curr_car != NULL)
    {
        printf("%s\n", curr_car -> value);
        curr_car = curr_car -> next;
    }
}


void cancel_train(struct car *first)
{
    if (first == NULL)
    {
        return;
    }
    cancel_train(first->next);
    free(first);
}


struct car *clear_train(struct car *first, const char *target)
{
    if (first == NULL)
    {
        return NULL;
    }
    if (strcmp(first -> value, target) == 0)
    {
        struct car *answer = first -> next;
        free(first);
        return answer;
    }

    struct car *prev_car = first;
    struct car *curr_car = first -> next;
    if (prev_car == NULL)
    {
        return first;
    }
    while ((prev_car -> next) != NULL) {
        curr_car = prev_car -> next;
        if(curr_car == NULL)
        {
            break;
        }
        // if found target
        if (strcmp(curr_car -> value, target) == 0)
        {
            // remove it and continue
            struct car *next_car = curr_car -> next;
            free(curr_car);
            prev_car -> next = next_car;
            prev_car = next_car;
        }
        else
        {
            prev_car = curr_car;
        }
        if (prev_car == NULL)
        {
            break;
        }
    }
    return first;
}