203. Remove Linked List Elements

Description of the Problem

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, 104].
1 <= Node.val <= 50
0 <= val <= 50

Solution

Tags: LinkedList

Code (C++)

/**
 * 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) {
        ListNode * dummyHead = new ListNode();
        dummyHead->next = head;
        
        ListNode * curr = dummyHead;
        
        while(curr != nullptr && curr->next != nullptr){
            if (curr->next->val == val) {
                curr->next = curr->next->next;
            }else{
                curr = curr->next;
            }
        }

        return dummyHead->next;
    }
};

Complexity

n is length of the linkedlist

Time Complexity:

\(T(n) = O(n)\)

Auxiliary Space:

\(S(n) = O(1) \)

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