程式碼隨想錄：設計連結串列

程式碼隨想錄：設計連結串列

這題遇到的問題是，在private中宣告後，在建構函式中初始化的時候又宣告瞭一次，大類的建構函式和結構體的建構函式弄暈掉了。

另外虛頭節點是真好用，以後記得用。

一開始寫成了這樣：

class MyLinkedList {
public:
    struct LinkNode {
        int value;
        LinkNode* next;
    };
    
    MyLinkedList() {
		    LinkNode* virtHead = new LinkNode();
		    virtHead->value = 0;
		    virtHead->next = NULL;

    _size = 0;
    }
    
    省略
private:
    int _size;
    LinkNode* virtHead;
};

正確程式碼如下：

class MyLinkedList {
public:
    struct LinkNode {
        int value;
        LinkNode* next;
    };

    MyLinkedList() {
        virtHead = new LinkNode();
        virtHead->value = 0;
        virtHead->next = NULL;

        _size = 0;
    }

    int get(int index) {
        // 遍歷連結串列，找到下標為index的節點
        if (index > _size - 1 || index < 0) {
            return -1;
        }
        LinkNode* target = virtHead;
        for (int i = 0; i < index + 1; i++) {
            target = target->next;
        }
        return target->value;
    }

    void addAtHead(int val) {
        LinkNode* insertNode = new LinkNode();
        insertNode->value = val;
        insertNode->next = virtHead->next;
        virtHead->next = insertNode;
        _size++;
    }

    void addAtTail(int val) {
        LinkNode* insertNode = new LinkNode();
        insertNode->value = val;
        insertNode->next = NULL;

        LinkNode* target = virtHead;
        while (target->next != NULL) {
            target = target->next;
        }

        target->next = insertNode;
        _size++;
    }

    void addAtIndex(int index, int val) {
        LinkNode* target = virtHead;
        if (index > _size) {
        } else {
            for (int i = 0; i < index; i++) {
                target = target->next;
            }

            LinkNode* insertNode = new LinkNode();
            insertNode->value = val;
            insertNode->next = target->next;

            target->next = insertNode;
            _size++;
        }
    }

    void deleteAtIndex(int index) {
        if (index > _size - 1 || index < 0) {
        } else {
            LinkNode* target = virtHead;
            for (int i = 0; i < index; i++) {
                target = target->next;
            }
            target->next = target->next->next;
            _size--;
        }
    }

private:
    int _size;
    LinkNode* virtHead;
};

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * MyLinkedList* obj = new MyLinkedList();
 * int param_1 = obj->get(index);
 * obj->addAtHead(val);
 * obj->addAtTail(val);
 * obj->addAtIndex(index,val);
 * obj->deleteAtIndex(index);
 */