203.Remove Linked List Elements

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Question

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

Example:

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Input:  1->2->6->3->4->5->6, val = 6
Output: 1->2->3->4->5

Answer

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
        while(head!=null&&head.val==val) //only one element and want to remove it
            head = head.next;
        ListNode temp = head;
        while(head!=null&&head.next!=null){
            if(head.next.val==val)
                head.next = head.next.next;
            else
                head = head.next;
        } 
        return temp;// notice some edge condition: [1,1] remove 1
    }
}

Some edge condition:

[] -remove-> [] null

[1,1] –remove 1–> []

[1] –remove 1–>[]

Recursive method

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public ListNode removeElements(ListNode head, int val) {
        if (head == null) return null;
        head.next = removeElements(head.next, val);
        return head.val == val ? head.next : head;
}