#Leetcode# 203. Remove Linked List Elements

/**
 * 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;
        head -> next = removeElements(head -> next, val);
        return head -> val == val ? head -> next : 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) {
        ListNode *dummy = new ListNode(-1), *pre = dummy;
        dummy -> next = head;
        while(pre -> next) {
            if(pre -> next -> val == val) {
                ListNode *t = pre -> next;
                pre -> next = t -> next;
                t -> next = NULL;
                delete t;
            }
            else pre = pre -> next;
        }
        return dummy -> next;
    }
};