Delete node in a Linked List

Problem Link

237. Delete Node in a Linked List – LeetCode

Problem Statement

There is a singly linked list, and you are given a node that is guaranteed not to be the tail of the list.

Delete the node from the list, but you will not be given access to the head of the list.

Examples

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 becomes 4 → 1 → 9 after calling your function.

Example 2:

Input: head = [4,5,1,9], node = 1
Output: [4,5,9]

Constraints

• The linked list will contain at least two nodes.

• The given node will not be the tail.

• All node values are unique.

Intuition

You don’t have access to the previous node, so you can't directly remove the current node like in a normal deletion process.

Instead, we can:

• Copy the value of the next node into the current node.

• Set node.next = node.next.next.

This simulates deleting the current node by replacing it with its next.

Approach

1. Copy the value of node.next to node.

2. Skip the node.next by setting node.next = node.next.next.

Java Code

class Solution {
    public void deleteNode(ListNode node) {
        node.val = node.next.val;
        node.next = node.next.next;
    }
}

Time and Space Complexity

Dry Run

Input:

List: 4 → 5 → 1 → 9, node = 5

Steps:

• node.val = node.next.val → node.val = 1

• node.next = node.next.next → skip the original 1

Output: 4 → 1 → 9

Conclusion

This is a tricky pointer manipulation problem where you're forced to think differently because you don’t have access to the previous node or the head.
It tests your understanding of what a "node" really represents in a linked list.