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Kathan Vakharia

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# LinkedList Questions: Delete a given node in constant time

In this series of posts, I will discuss coding questions on the `LinkedList` Data structure.
The posts in this series will be organized in the following way,

2. Possible Explanation ๐
3. Documented C++ Code ๐งน
4. Time and Space Complexity Analysis โ๐

## The Question

Write a function to delete a node in a singly-linked list. You will not be given access to the `head` of the list, instead you will be given access to the node to be deleted directly.

It is guaranteed that the node to be deleted is not a tail node in the list.

๐ก Give yourself atleast 5 mins to figure out the solution :)

## Explanation

It is a warm-up question, there's not much to explain,

1. Copy the data of the next node into the given node.
2. Make the given node point to the next's neighbor.
3. Free up the old neighbor of the given node.

## C++ Code

``````//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) {}
};
``````

### Solution

``````#include <bits/stdc++.h>
using namespace std;

/*
-Time:O(1)
-Space:O(1)
*/
class Solution
{
public:
//! given node isn't the "tail" node
void deleteNode(ListNode *node)
{
ListNode *temp = node->next;

//I can do this only because node isn't the tail node
//and "node->next" will not null therefore
node->val = node->next->val;
node->next = node->next->next;

delete temp;
}
};

``````

## Complexity Analysis

### Time Complexity: O(1)

No iteration or recursion is done.

### Space Complexity: O(1)

No extra space is used.