1 Description #
Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head.
Example 1:
Input: head = [1,2,6,3,4,5,6], val = 6
Output: [1,2,3,4,5]
Example 2:
Input: head = [], val = 1
Output: []
Example 3:
Input: head = [7,7,7,7], val = 7
Output: []
Constraints:
- The number of nodes in the list is in the range
[0, 10^4]. 1 <= Node.val <= 500 <= val <= 50
2 Solution #
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
ListNode* removeElements(ListNode* head, int val) {
// Time complexity: O(N), N is the size of linked list
// Space complexity: O(1)
if(!head){
return head;
}
ListNode* prev = nullptr;
ListNode* result = nullptr;
while(head){
if(head->val == val){
if(prev){
prev->next = head->next;
head = head->next;
}else{
ListNode* next = head->next;
head->next = nullptr;
head = next;
}
}else{
prev = head;
head = head->next;
}
result = (result ==nullptr? prev: result);
}
return result;
}
};