###### Copy List with Random Pointer | February Leetcoding challenge 2021 | Day 10
Manas Sinha
Developer | Designer

## Copy List with Random Pointer

`PROBLEM  STATEMENT:`
A linked list of length `n` is given such that each node contains an additional random pointer, which could point to any node in the list, or `null`.
Construct a deep copy of the list. The deep copy should consist of exactly `n` brand new nodes, where each new node has its value set to the value of its corresponding original node. Both the `next` and `random` pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list.
For example, if there are two nodes `X` and `Y` in the original list, where `X.random --> Y`, then for the corresponding two nodes `x` and `y` in the copied list, `x.random --> y`.

The linked list is represented in the input/output as a list of `n` nodes. Each node is represented as a pair of `[val, random_index]` where:
• `val`: an integer representing `Node.val`
• `random_index`: the index of the node (range from `0` to `n-1`) that the `random` pointer points to, or `null` if it does not point to any node.
Your code will only be given the `head` of the original linked list.

Example 1
```
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]
```
Example 2
```
Output: [[1,1],[2,1]]
```
Example 3
```
Output: [[3,null],[3,0],[3,null]]
```
Constraints:
• `0 <= n <= 1000`
• `-10000 <= Node.val <= 10000`
• `Node.random` is `null` or is pointing to some node in the linked list.

## Explanation

Using constant extra space:
`ALGORITHM: `
• Create the copy of every node and insert it next to the original one. Eg:copy of node1 will go between node1 and node2 of original list.
• Now copy the random pointer in the following way : `original->next->random = original->random->next;`
• Restore the copy of the list : ```original->next = original->next->next; copy->next = copy->next->next;```

## code

``````public:
while(temp!=NULL)
{
Node* node_copy = new Node(temp->val);
node_copy->next = temp->next;
temp->next = node_copy;
temp = node_copy->next;
}

while(temp!=NULL)
{
if(temp->random) temp->next->random = temp->random->next;
temp = temp->next->next;
}
while(temp!=NULL)
{

temp->next = grip->next;
temp = temp->next;
grip->next = temp ? temp->next : NULL;
grip = grip ? grip->next : NULL;
}
return grip_h;
}
};``````