c - 将存储为链表的两个数字相加 - 无法使用 C 解决

Question

我理解了这个问题，但我无法用“C”解决它。

struct ListNode* newnode(struct ListNode* node, int data) {
    struct ListNode* temp = node;
    struct ListNode* newnode = (struct ListNode*)malloc(sizeof(struct ListNode));    
    while (temp->next != NULL) {
        temp = temp->next;
    }
    temp->next = newnode;
    newnode->next = NULL;
    newnode->val = data;
    return newnode;
}  

struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2) {
    struct ListNode* l;
    struct ListNode* temp = l;

    int carry = 0;
    while (l1 != NULL || l2 != NULL) {
        int sum = 0;
        if (l1 != NULL) {
            sum += l1->val;
            l1 = l1->next;
        }
        if (l2 != NULL) {
            sum += l2->val;
            l2 = l2->next;
        }
        if (sum >= 10) {    
            temp  = newnode(l, carry);
            carry = sum % 10;
        }
        else {
            temp = newnode(l, carry + sum);
        }
    }       
    return l;
}

出现运行时错误:“struct ListNode”类型的空指针内的成员访问(solution.c)。我单独运行了“newnode”函数，效果很好。

需要帮助，只是初学者。

Answer 1

处理将新节点添加到空列表:

struct ListNode* newnode(struct ListNode* node, int data){

    struct ListNode* temp = node;
    struct ListNode *newnode = (struct ListNode*)malloc(sizeof(struct ListNode));

    if(temp == NULL){
       newnode->val = data;
       newnode->next = NULL;
       return newnode;
    }
    while(temp->next != NULL){
        temp = temp->next;
    }
    temp->next = newnode;
    newnode->next = NULL;
    newnode->val = data;

    return newnode;
}