LeetCode 203. 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

/**
 * 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 != NULL && head->val == val) {
            head = head->next;
        }
        if(head == NULL) {
            return NULL;
        }
        ListNode *p = head;
        ListNode *q= p->next;
        while(p != NULL && p->next != NULL) {
            q = p->next;
            while(q != NULL && q->val == val) {
                q = q->next;
            }
            p->next = q;
            p = q;
        }
        return head;
    }
};

/**

* 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 != NULL && head->val == val) {

head = head->next;

}

if(head == NULL) {

return NULL;

}

ListNode *p = head;

ListNode *q= p->next;

while(p != NULL && p->next != NULL) {

q = p->next;

while(q != NULL && q->val == val) {

q = q->next;

}

p->next = q;

p = q;

}

return head;

}

};

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