算法: 刪除鏈表中的數據Remove Linked List Elements

題目

203. Remove Linked List Elements

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

Example:

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

Iteration 遍歷執行

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
       ListNode fakeHead = new ListNode(-1);
        fakeHead.next = head;
        ListNode pre = fakeHead;
        while (head != null) {
          if (head.val == val) {
            pre.next = head.next;
          } else {
            pre = head;
          }
          head = head.next;
        }
        return fakeHead.next;
    }
}

Recursive遞歸執行

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
        // exit condition
    if (head == null) return null;
    // recursive from tail to head.
    head.next = removeElements(head.next, val);
    return head.val == val ? head.next : head;
    }
}