Remove Linked List Element

题目：

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

分析：

简单题目没啥好分析的，画画图，验证验证，保证别出错，一次通过就好了。

解法：

class Solution {
public:
    /**
     * @param head a ListNode
     * @param val an integer
     * @return a ListNode
     */
    ListNode *removeElements(ListNode *head, int val) {
        // Write your code here
        if (head == NULL) {
            return head;
        }

        ListNode dummy(val - 1);
        dummy.next = head;

        ListNode* prev = &dummy;
        ListNode* curr = head;

        while (curr != NULL) {
            if (curr->val == val) {
                curr = curr->next;
                prev->next = curr;
            } else {
                prev = prev->next;
                curr = curr->next;
            }
        }

        return dummy.next;
    }
};