Leecode 203. 移除链表元素

原题链接：Leecode 203. 移除链表元素


迭代·:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        if(head==nullptr) return nullptr;
        while(head && head->val==val)
        {
            head=head->next;
        }
        ListNode* root=head;
        while(head && head->next)
        {
            if(head->next->val==val)  head->next=head->next->next;
            else head=head->next;
        }
        return root;
    }
};

递归:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) {
        if(head==nullptr) return nullptr;
        head->next=removeElements(head->next, val);
        head= head->val==val ? head->next:head;
        return head;
    }
};