# info2021-homework2
###### tags : `資訊科技產業面試`
:::warning
英文版只有稍加修飾，與加上一題新的題目
中文版是全新的版本
:::

### interviewer 自評
1. 比上次能有更多的敘述
2. 能中斷面試者的過程
3.

### interviewee
1. 會對問題的內容有更多的提問，像是node 的資料型別等等
2. 對資料結構的名詞適用不夠確切
3.

### question1 :

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

class Solution {
public:
    int getDecimalValue(ListNode* head) {
        int sum = 0 ;
        ListNode* pointer= head;
        while(pointer != NULL){
            sum = sum *2 ;
            sum = sum + pointer->val;
            pointer= pointer->next;
        }
        return sum;
    }
};

### question2 :

class Solution {
public:
    ListNode* deleteNodes(ListNode* head, int m, int n) {
        ListNode* pointer=head;
        int remove = n;
        int keep = m-1 ; 
        while(pointer != NULL){
            if(keep != 0){
                pointer = pointer->next;
                keep--;
            }else if(remove != 0){
                if(pointer->next == NULL) break; 
                pointer->next = pointer->next->next;
                remove--;
            }else{
                keep = m;
                remove = n ;
            }
        }
        return head;
        
    }
};

### question3:
這題有一個利用 pointer to pointer的寫法

ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        int sum=0;
        ListNode *head, *tail_pointer;
        ListNode* node = new ListNode; // new struct ListNode 跟 new ListNode 一樣
        head = node;
        tail_pointer = node;
        while(l1 != NULL || l2 !=NULL || sum != 0){
            if(l1 != NULL){
                sum = sum + l1->val;
                l1 = l1->next;
            }
            if(l2 != NULL){
                sum = sum + l2->val;
                l2 = l2->next;
            }
            tail_pointer->val = sum%10;
            sum = sum/10;
            if(l1 != NULL || l2 !=NULL || sum != 0){
                ListNode* node = new ListNode;
                tail_pointer->next = node;
                tail_pointer = tail_pointer->next;
            }    
        }
        return head;
    }