Leetcode: Remove Linked List Elements


Remove all elements from a linked list of integers that have value val.

Example
Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6
Return: 1 --> 2 --> 3 --> 4 --> 5

简单。

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeElements(ListNode* head, int val) {
while (head != nullptr && head->val == val) {
head = head->next;
}
if (head == nullptr) {
return head;
}

ListNode* prev = head;
ListNode* cur = head->next;
while (cur != nullptr) {
if (cur->val != val) {
prev->next = cur;
prev = cur;
}
cur = cur->next;
}
prev->next = nullptr;

return head;
}
};

Hack的方法，直接移动值。

/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeElements(ListNode* head, int val) {
ListNode* cur = head;
ListNode* prev = head;
ListNode* tail = nullptr;
while (cur != nullptr) {
if (cur->val != val) {
prev->val = cur->val;
tail = prev;
prev = prev->next;
}
cur = cur->next;
}
if (tail != nullptr) {
tail->next = nullptr;
}
else {
head = nullptr;
}

return head;
}
};