leetcode Question: Remove Linked List Elements

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

Analysis:

This is a fundamental pointer manipulation question.
Just be careful with the case that removing 1st element. In the code below, a new pointer is assigned to link to the 1st element.


Code(C++):

/**
 * 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) {
        if (!head) return NULL;
        ListNode *h = new ListNode(0);
        h->next = head;
        head = h;
        while (h->next){
            if (h->next->val == val){
                h->next = h->next->next;
            }else{
                h = h->next;
            }
        }
        return head->next;
    }
};

Code(Python):

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @param {ListNode} head
    # @param {integer} val
    # @return {ListNode}
    def removeElements(self, head, val):
        if not head:
            return None
        h = ListNode(0)
        h.next = head
        head = h
        while h.next:
            if h.next.val == val:
                h.next = h.next.next
            else:
                h = h.next
        return head.next