LeetCode - Remove Linked List Elements

Remove Linked List Elements

2015.4.30 15:00

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

Solution:

　　Watch out for boundary cases.

Accepted code:

// 1AC, no surprise
/**
 * 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 *ptr;
        
        while (head != NULL && head->val == val) {
            ptr = head;
            head = head->next;
            delete ptr;
        }
        
        ListNode *head0 = head;
        
        if (head0 == NULL) {
            return NULL;
        }
        
        while (head->next != NULL) {
            if (head->next->val == val) {
                ptr = head->next;
                head->next = ptr->next;
                delete ptr;
            } else {
                head = head->next;
            }
        }
        
        return head0;
    }
};