List

143. Reorder List

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def reorderList(self, head: ListNode) -> None:
        """
        Do not return anything, modify head in-place instead.
        """
        if head is None:return
        nodes = []
        node = head
        while True:
            nodes.append(node)
            if node.next is None:break
            node = node.next
        N = len(nodes)
        i, j = 0, N-1
        count = 0 
        a, b = nodes[i], nodes[j]
        while True:
            if count==N-1:
                a.next =None
                break
            a.next = b
            b.prev = a
            count += 1
            a = b
            if count%2==1:
                i += 1
                b = nodes[i] 
            else:
                j-=1
                b =  nodes[j]

237. Delete Node in a Linked List

C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void deleteNode(ListNode* node) {
        while (true)
        {
            node->val = node->next->val;
            if (!node->next->next)
            {
                node->next = nullptr;
                break;
            }
            node = node->next;
        }
        return;        
    }
};

Or more efficient

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void deleteNode(ListNode* node) {
        node->val = node->next->val;
        node->next = node->next->next;
        return;
    }
};

Python

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def deleteNode(self, node):
        """
        :type node: ListNode
        :rtype: void Do not return anything, modify node in-place instead.
        """
        node.val = node.next.val
        node.next = node.next.next

203. Remove Linked List Elements

C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeElements(ListNode* head, int val) 
    {
        if (!head)return head;
        if(head->val==val)return removeElements(head->next, val);
        else
        {
            head->next = removeElements(head->next, val);
            return head;
        }   
    }
};