707. Design Linked List

  1 class MyLinkedList {
  2 public:
  3     struct ListNode {
  4         int val;
  5         int length;
  6         ListNode *tail;
  7         ListNode *next;
  8         ListNode(int n = 0):val(n), length(0), tail(nullptr), next(nullptr){}
  9     };
 10     
 11     /** Initialize your data structure here. */
 12     MyLinkedList() {
 13         pHead = new ListNode(-1);
 14     }
 15     
 16     /** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
 17     int get(int index) {
 18         if (index >= pHead->length || index < 0) return -1;
 19         
 20         ListNode *p = pHead->next;
 21         for (int i = 0; i < index; ++i)
 22         {
 23             p = p->next;
 24         }
 25         
 26         return p->val;
 27     }
 28     
 29     /** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
 30     void addAtHead(int val) {
 31         ListNode *pNew = new ListNode(val);
 32         if (pHead->next == nullptr)
 33         {
 34             
 35             pHead->tail = pNew;
 36         }
 37         
 38         pNew->next = pHead->next;
 39         pHead->next = pNew;
 40         
 41         pHead->length++;
 42     }
 43     
 44     /** Append a node of value val to the last element of the linked list. */
 45     void addAtTail(int val) {
 46         ListNode *pTail = new ListNode(val);
 47         if (pHead->tail == nullptr)
 48         {
 49             pHead->tail = pTail;
 50             pTail->next = pHead->next;
 51             pHead->next = pTail;
 52         }
 53         else
 54         {
 55             pHead->tail->next = pTail;
 56             pHead->tail = pTail;
 57         }
 58         
 59         pHead->length++;
 60     }
 61     
 62     /** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
 63     void addAtIndex(int index, int val) {
 64         if (index == pHead->length)     // equal
 65         {
 66             addAtTail(val);
 67         }
 68         else if (index > pHead->length)
 69         {
 70             return;
 71         }
 72         else
 73         {
 74             ListNode *p = pHead->next;
 75             for (int i = 0; i < index - 1; ++i)
 76             {
 77                 p = p->next;
 78             }
 79             
 80             ListNode *pNew = new ListNode(val);
 81             pNew->next = p->next;
 82             p->next = pNew;
 83             
 84             pHead->length++;
 85         }
 86         
 87     }
 88     
 89     /** Delete the index-th node in the linked list, if the index is valid. */
 90     void deleteAtIndex(int index) {
 91         if (index >= pHead->length || index < 0) return;
 92         
 93         ListNode *p = pHead->next;
 94         for (int i = 0; i < index - 1; ++i)
 95         {
 96             p = p->next;
 97         }
 98     
 99         if (index == pHead->length - 1)
100         {
101             pHead->tail = p;
102         }
103         
104         ListNode *del = p->next;
105         p->next = del->next;
106         pHead->length--;
107         
108         del->tail = nullptr;
109         del->next = nullptr;
110         delete del;
111     }
112     
113 private:
114     ListNode *pHead;
115 };
116 
117 /**
118  * Your MyLinkedList object will be instantiated and called as such:
119  * MyLinkedList obj = new MyLinkedList();
120  * int param_1 = obj.get(index);
121  * obj.addAtHead(val);
122  * obj.addAtTail(val);
123  * obj.addAtIndex(index,val);
124  * obj.deleteAtIndex(index);
125  */