[刷题] 203 Remove Linked List Elements

要求

• 在链表中删除值为val的所有节点

示例

• 如 1->2->3->4->5->6->NULL，要求删除值为6的节点
• 返回1->2->3->4->5->NULL

思路

• 删除一般元素（包括最后一个元素）
• 删除第一个元素

实现

• 常规思路

 1 #include <iostream>
 2 using namespace std;
 3
 4 struct ListNode {
 5     int val;
 6     ListNode *next;
 7     ListNode(int x) : val(x), next(NULL) {}
 8 };
 9
10 ListNode* createLinkedList(int arr[], int n){
11     if( n == 0 )
12         return NULL;
13     ListNode* head = new ListNode(arr[0]);
14     ListNode* curNode = head;
15     for( int i = 1 ; i < n ; i ++ ){
16         curNode->next = new ListNode(arr[i]);
17         curNode = curNode->next;
18     }
19     return head;
20 }
21
22 void printLinkedList(ListNode* head){
23     ListNode* curNode = head;
24     while( curNode != NULL ){
25         cout << curNode->val << " -> ";
26         curNode = curNode->next;
27     }
28     cout<<"NULL"<<endl;
29     return;
30 }
31
32 void deleteLinkedList(ListNode* head){
33     ListNode* curNode = head;
34     while( curNode != NULL){
35         ListNode* delNode = curNode;
36         curNode = curNode->next;
37         delete delNode;
38     }
39     return;
40 }
41
42 class Solution {
43 public:
44     ListNode* removeElements(ListNode* head, int val) {
45
46         while( head != NULL && head->val == val ){
47             ListNode* delNode = head;
48             head = delNode->next;
49             delete delNode;
50         }
51
52         if( head == NULL )
53             return NULL;
54
55         ListNode* cur = head;
56         while( cur->next != NULL ){
57
58             if( cur->next->val == val ){
59                 ListNode* delNode = cur->next;
60                 cur->next = delNode->next;
61                 delete delNode;
62             }else
63                 cur = cur->next;
64         }
65         return head;
66     }
67 };
68
69 int main(){
70     int arr[] = {1,2,3,4,5};
71     int n = sizeof(arr)/sizeof(int);
72
73     ListNode* head = createLinkedList(arr,n);
74     Solution().removeElements(head,3);
75     printLinkedList(head);
76
77     deleteLinkedList(head);
78     return 0;
79 }

• 设置虚拟头节点

 1 #include <iostream>
 2 using namespace std;
 3
 4 struct ListNode {
 5     int val;
 6     ListNode *next;
 7     ListNode(int x) : val(x), next(NULL) {}
 8 };
 9
10 ListNode* createLinkedList(int arr[], int n){
11     if( n == 0 )
12         return NULL;
13     ListNode* head = new ListNode(arr[0]);
14     ListNode* curNode = head;
15     for( int i = 1 ; i < n ; i ++ ){
16         curNode->next = new ListNode(arr[i]);
17         curNode = curNode->next;
18     }
19     return head;
20 }
21
22 void printLinkedList(ListNode* head){
23     ListNode* curNode = head;
24     while( curNode != NULL ){
25         cout << curNode->val << " -> ";
26         curNode = curNode->next;
27     }
28     cout<<"NULL"<<endl;
29     return;
30 }
31
32 void deleteLinkedList(ListNode* head){
33     ListNode* curNode = head;
34     while( curNode != NULL){
35         ListNode* delNode = curNode;
36         curNode = curNode->next;
37         delete delNode;
38     }
39     return;
40 }
41
42 class Solution {
43 public:
44     ListNode* removeElements(ListNode* head, int val) {
45
46         ListNode* dummyHead = new ListNode(0);
47         dummyHead->next = head;
48
49         ListNode* cur = dummyHead;
50         while( cur->next != NULL ){
51
52             if( cur->next->val == val ){
53                 ListNode* delNode = cur->next;
54                 cur->next = delNode->next;
55                 delete delNode;
56             }else
57                 cur = cur->next;
58         }
59
60         ListNode* retNode = dummyHead->next;
61         delete dummyHead;
62
63         return retNode;
64     }
65 };
66
67 int main(){
68     int arr[] = {1,2,3,4,5};
69     int n = sizeof(arr)/sizeof(int);
70
71     ListNode* head = createLinkedList(arr,n);
72     Solution().removeElements(head,3);
73     printLinkedList(head);
74
75     deleteLinkedList(head);
76     return 0;
77 }

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