題目

刪除連結串列中等於給定值 val 的所有節點。

示例:

輸入: 1->2->6->3->4->5->6, val = 6 輸出: 1->2->3->4->5

思路

1. 判斷head是否為空
2. 判斷head.val是否等於val
3. 構造兩個節點，一個等於當前節點，一個等於當前節點的上一個節點，便於刪除節點

python程式碼

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        if head == None:
            return head
        while head != None and head.val == val:
            head = head.next
        if head == None:
            return head
        L = ListNode(0)
        L2 = ListNode(0)
        L1 = head
        while L1 != None:
            if L1.val == val:
                L2.next = L1.next
                L1 = L1.next
            else:
                L2 = L1
                L1 = L1.next
        return head
                
        
 

java程式碼

/**
 * 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)
        {
            while(head != null && head.val == val)
            {
                head = head.next;
            }
            if(head != null)
            {
                ListNode L1 = new ListNode(0);
                ListNode L2 = new ListNode(0);
                L1 = head;
                while(L1 != null)
                {
                    if (L1.val == val)
                    {
                        L2.next = L1.next;
                        L1 = L1.next;
                    }
                    else
                    {
                        L2 = L1;
                        L1 = L1.next;
                    }
                }
            }
        }
        
        return head;
    }
}