LeetCode-Remove Linked List Elements-解題報道

原題鏈接https://leetcode.com/problems/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 

就是刪除鏈表中所有對應值的節點。

先看是否需要刪除頭，然後在判斷中間的。

/**
 * 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 == NULL)return NULL;
		ListNode *pre, *current;
		pre = head;
		current = head->next;
		while (pre != NULL && pre->val == val)
		{
			pre = current;
			if (pre != NULL)
				current = pre->next;
		}
		head = pre;
		while (current != NULL)
		{
			if (current->val == val)
				pre->next = current->next;
			
			else
				pre = current;
			current = current->next;
		}
		return head;
	}
};