[LintCode] Remove Linked List Elements 移除链表元素

Remove all elements from a linked list of integers that have value val.

Have you met this question in a real interview?

Example

Given 1->2->3->3->4->5->3, val = 3, you should return the list as 1->2->4->5

LeetCode上的原题，请参见我之前的博客Remove Linked List Elements。

解法一：

class Solution {
public:
    /**
     * @param head a ListNode
     * @param val an integer
     * @return a ListNode
     */
    ListNode *removeElements(ListNode *head, int val) {
        ListNode *dummy = new ListNode(-), *pre = dummy;
        dummy->next = head;
        while (pre->next) {
            if (pre->next->val == val) {
                ListNode *t = pre->next;
                pre->next = t->next;
                t->next = NULL;
            } else {
                pre = pre->next;
            }
        }
        return dummy->next;
    }
};

解法二：

class Solution {
public:
    /**
     * @param head a ListNode
     * @param val an integer
     * @return a ListNode
     */
    ListNode *removeElements(ListNode *head, int val) {
        if (!head) return NULL;
        head->next = removeElements(head->next, val);
        return head->val == val ? head->next : head;
    }
};