第二十九题：LeetCode203号问题，删除链表中的指定元素(Java)

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题目：

从具有值val的整数的链接列表中删除所有元素。例：

输入：   1-> 2-> 6-> 3-> 4-> 5-> 6，val = 6
输出： 1-> 2-> 3-> 4-> 5

Solution代码：

/**
 * 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) {
            if (head == null){
            return null;
        }
        ListNode res = removeElements(head.next, val);
        if (head.val == val){
            return res;
        }else {
            head.next = res;
            return head;
        }
    }
}

测试代码：

package com.isea.spark.java_way;

public class ListNode {
    int val;
    ListNode next;
    ListNode(int x){
        val = x;
    }

    public ListNode(int[] arr){
        if (arr.length == 0 || arr == null){
            throw new IllegalArgumentException("The Array is null...");
        }
        this.val = arr[0];
        ListNode cur = this;

        for (int i = 1; i < arr.length; i++) {
            cur.next = new ListNode(arr[i]);
            cur = cur.next;
        }
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        ListNode cur = this;
        while(cur != null){
            res.append(cur.val + "->");
            cur = cur.next;
        }
        res.append("NULL");
        return res.toString();
    }


}

class Solution{
    public  ListNode removeElements(ListNode head, int val) {
        if (head == null){
            return null;
        }
        ListNode res = removeElements(head.next, val);
        if (head.val == val){
            return res;
        }else {
            head.next = res;
            return head;
        }
    }

    public static void main(String[] args) {
        int[] nums = {1,2,6,3,4,5,6};
        ListNode head = new ListNode(nums);
        System.out.println(head);

        ListNode res = new Solution().removeElements(head, 6);
        System.out.println(res);
        /**
         * 1->2->6->3->4->5->6->NULL
         * 1->2->3->4->5->NULL
         */
    }
}