问在双向链表上使用冒泡排序

EN

//
//  Double_linked_list.c
//
//
//  Created by Dengke Liu on 9/7/15.
//
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#include "list.h"


// initialize the list structure;
void init(slist_t *list){
    list->head=NULL;
    list->tail=NULL;
}

// add a string to the end of the list
void append(slist_t *list, char *val){

    // creating a newItem object
    list_item_t* newItem = (list_item_t*)malloc(sizeof(list_item_t));
    newItem->value = val;
    newItem->next=NULL;

    // if there are no elements, just use newItem as head
    if (!list->head) {
        newItem->prev=NULL;
        list->head=newItem;
        list->tail=newItem;
    }else{
        // otherwise append the node and point the tail at the end
        newItem->prev=list->tail;
        list->tail->next=newItem;
        list->tail=newItem;
    }
}

// print the elements of the list
void print(slist_t *list){

    list_item_t* temp=list->head;
    while (temp!=NULL) {
        printf("%s\n", temp->value);
        temp=temp->next;
    }
}

// empty the list
void empty(slist_t *list){

    list_item_t *temp=list->head;
    while (temp->next!=NULL) {
        temp=temp->next;
        free(temp);
    }
    free(list->head);
}

// sort the elements in list in lexical order using bubble sort
void bubblesort(slist_t *list){

    if (list->head==NULL) {
        printf("this is an empty list");
    }

    // to record the comparision state
    bool swapped=true;
    list_item_t *temp;

    while (swapped) {

        swapped=false;
        temp=list->head;

        // iterate through the list to swap unordered elements
        while (temp!=list->tail) {
            // compare two elements, if they are disordered, then swap
            if(strcmp(temp->value, temp->next->value)>0){

                // swap the elements
                if (temp->prev!=NULL) {
                    temp->prev->next=temp->next;
                }
                if (temp->next->next!=NULL) {
                    temp->next->next->prev=temp;
                }

                temp->next=temp->next->next;
                temp->next->next=temp->prev;
                temp->next->next=temp;
                temp->prev=temp->next;

                // change the swap record
                swapped=true;
            }
            temp=temp->next;
        }

        print(list);
    }
}

int main(){
    slist_t *list;
    init(list);
    append(list, "blue");
    append(list, "yellow");
    append(list, "black");
    append(list, "red");
    append(list, "green");
    print(list);
    bubblesort(list);
    print(list);
    empty(list);
    return 0;
}