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Delete Node in a Linked List

LeetCode 237 | Difficulty: Medium​

Medium

Problem Description​

There is a singly-linked list head and we want to delete a node node in it.

You are given the node to be deleted node. You will not be given access to the first node of head.

All the values of the linked list are unique, and it is guaranteed that the given node node is not the last node in the linked list.

Delete the given node. Note that by deleting the node, we do not mean removing it from memory. We mean:

- The value of the given node should not exist in the linked list.

- The number of nodes in the linked list should decrease by one.

- All the values before `node` should be in the same order.

- All the values after `node` should be in the same order.

Custom testing:

- For the input, you should provide the entire linked list `head` and the node to be given `node`. `node` should not be the last node of the list and should be an actual node in the list.

- We will build the linked list and pass the node to your function.

- The output will be the entire list after calling your function.

Example 1:

Input: head = [4,5,1,9], node = 5
Output: [4,1,9]
Explanation: You are given the second node with value 5, the linked list should become 4 -> 1 -> 9 after calling your function.

Example 2:

Input: head = [4,5,1,9], node = 1
Output: [4,5,9]
Explanation: You are given the third node with value 1, the linked list should become 4 -> 5 -> 9 after calling your function.

Constraints:

- The number of the nodes in the given list is in the range `[2, 1000]`.

- `-1000 <= Node.val <= 1000`

- The value of each node in the list is **unique**.

- The `node` to be deleted is **in the list** and is **not a tail** node.

Topics: Linked List

Approach​

Linked List​

Use pointer manipulation. Common techniques: dummy head node to simplify edge cases, fast/slow pointers for cycle detection and middle finding, prev/curr/next pattern for reversal.

When to use

In-place list manipulation, cycle detection, merging lists, finding the k-th node.

Solutions​

Solution 1: C# (Best: 162 ms)​

MetricValue
Runtime162 ms
MemoryN/A
Date2017-09-22
Solution
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void DeleteNode(ListNode node) {
        node.val = node.next.val;
        node.next = node.next.next;
    }
}

Complexity Analysis​

ApproachTimeSpace
Linked List$O(n)$$O(1)$

Interview Tips​

Key Points
  • Discuss the brute force approach first, then optimize. Explain your thought process.
  • Draw the pointer changes before coding. A dummy head node simplifies edge cases.