本题要求实现两个函数，分别将读入的数据存储为单链表、将链表中偶数值的结点删除。链表结点定义如下：

struct ListNode { int data; struct ListNode *next; };

函数接口定义：

struct ListNode *createlist(); struct ListNode *deleteeven( struct ListNode *head ); 

函数createlist从标准输入读入一系列正整数，按照读入顺序建立单链表。当读到−1时表示输入结束，函数应返回指向单链表头结点的指针。

函数deleteeven将单链表head中偶数值的结点删除，返回结果链表的头指针。

 

void push_back(struct ListNode** ppList, int x)
{
    //assert(ppList != NULL);
    struct ListNode* newNode = (struct ListNode*)malloc(sizeof(struct ListNode));
    newNode->data = x;
    newNode->next = NULL;
    
    if (*ppList == NULL)
    {
        *ppList = newNode;
        return;
    }

    struct ListNode* end = *ppList;
    
    while (end->next != NULL)
    {
        end = end->next;
    }
    
    end->next = newNode;
}

struct ListNode* createlist()
{
    struct ListNode* head = (struct ListNode*)malloc(sizeof(struct ListNode));
    int ret = 0;
    scanf("%d", &ret);
    if (ret != -1)
    {
        head->data = ret;
        head->next = NULL;
    }
    else
    {
        free(head);
        return NULL;
    }
    
    while (1)
    {
        scanf("%d", &ret);
        if (ret == -1)
        {
            break;
        }
        
        push_back(&head, ret);
    }

    return head;
}

struct ListNode* deleteeven(struct ListNode* head)
{
    struct ListNode* prev = head;
    struct ListNode* cur = head;
    
    while (cur != NULL)
    {
        if (cur->data % 2 == 1)
        {
            prev = cur;
            cur = cur->next;
            continue;
        }
        
        if (prev == cur)
        {
            cur = cur->next;
            free(prev);
            prev = cur;
            head = cur;
            continue;
        }
        
        prev->next = cur->next;
        free(cur);
        cur = prev->next;
    }

    return head;
}