一、使用虚拟头结点

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @param val int整型 
     * @return ListNode类
     */
    public ListNode deleteNode (ListNode head, int val) {
        // write code here
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode pre = dummy;
        ListNode cur = dummy.next;
        ListNode tmp = null;
        while(cur != null){
            tmp = cur.next;
            if(cur.val == val){
                pre.next = tmp;
                break;
            }
            pre = cur;
            cur = tmp;
        }
        return dummy.next;
    }
}

二、不使用虚拟头结点

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @param val int整型 
     * @return ListNode类
     */
    public ListNode deleteNode (ListNode head, int val) {
        // write code here
        ListNode pre = null;
        ListNode cur = head;
        ListNode tmp = null;
        while(cur != null){
            tmp = cur.next;
            if(cur.val == val){
                if(cur == head) return head.next;
                pre.next = tmp;
                return head;
            }
            pre = cur;
            cur = tmp;
        }
        return null;
    }
}