## Algorithm

Problem Name: 138. Copy List with Random Pointer

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:

```Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]
```

Example 2:

```Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]
```

Example 3:

```Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]
```

Constraints:

• `0 <= n <= 1000`
• `-104 <= Node.val <= 104`
• `Node.random` is `null` or is pointing to some node in the linked list.

## Code Examples

### #1 Code Example with C Programming

```Code - C Programming```

``````
struct RandomListNode *copyRandomList(struct RandomListNode *head) {
struct RandomListNode **srcstack;
struct RandomListNode **dststack;
int *flagstack, found_cycle = 0;
int i, sp = 1, sz = 100;
struct RandomListNode *ret = NULL, *newnode, *newrandom, **prevp = NULL;
struct RandomListNode *node = head, *random;

srcstack = malloc(sz * sizeof(struct RandomListNode *));
dststack = malloc(sz * sizeof(struct RandomListNode *));
flagstack = malloc(sz * sizeof(int));
//assert(srcstack && dststack && flagstack);
srcstack[0] = dststack[0] = NULL;

while (node) {
i = 1;
while (i  <  sp && srcstack[i] != node) {
i ++;
}
if (i == sp) {
newnode = malloc(sizeof(struct RandomListNode));
//assert(newnode);
newnode->label = node->label;
newnode->next = NULL;
newnode->random = NULL;
if (sp == sz) {
sz = sz * 2;
srcstack = realloc(srcstack, sz * sizeof(struct RandomListNode *));
dststack = realloc(dststack, sz * sizeof(struct RandomListNode *));
flagstack = realloc(flagstack, sz * sizeof(int));
//assert(srcstack && dststack && flagstack);
}
srcstack[sp] = node;
dststack[sp] = newnode;
flagstack[sp] = 1;
sp ++;
} else {
newnode = dststack[i];
found_cycle = flagstack[i];
flagstack[i] = 1;
}

if (!ret) ret = newnode;

if (prevp) *prevp = newnode;
prevp = &newnode->next;

//if (found_cycle) break;

random = node->random;
i = 0;
while (i  <  sp && srcstack[i] != random) {
i ++;
}
if (i == sp) {
newrandom = malloc(sizeof(struct RandomListNode));
//assert(newrandom);
newrandom->label = random->label;
newrandom->next = NULL;
newrandom->random = NULL;
if (sp == sz) {
sz = sz * 2;
srcstack = realloc(srcstack, sz * sizeof(struct RandomListNode *));
dststack = realloc(dststack, sz * sizeof(struct RandomListNode *));
flagstack = realloc(flagstack, sz * sizeof(int));
//assert(srcstack && dststack && flagstack);
}
srcstack[sp] = random;
dststack[sp] = newrandom;
flagstack[sp] = 0;
sp ++;
} else {
newrandom = dststack[i];
}
newnode->random = newrandom;

node = node->next;
}

free(srcstack);
free(dststack);

return ret;
}
``````
Copy The Code &

Input

cmd

Output

cmd
[[7,null],[13,0],[11,4],[10,2],[1,0]]

### #2 Code Example with C++ Programming

```Code - C++ Programming```

``````
class Solution {
public:
unordered_mapm;
while(p){
m[p] = new RandomListNode(p->label);
p = p->next;
}
while(p){
m[p]->next = m[p->next];
m[p]->random = m[p->random];
p = p->next;
}
}
};
``````
Copy The Code &

Input

cmd

Output

cmd
[[7,null],[13,0],[11,4],[10,2],[1,0]]

### #3 Code Example with Java Programming

```Code - Java Programming```

``````
class Solution {
}

while (curr != null) {
Node newNode = new Node(curr.val);
newNode.next = curr.next;
curr.next = newNode;
curr = newNode.next;
}

while (curr != null) {
curr.next.random = curr.random != null ? curr.random.next : null;
curr = curr.next.next;
}
// Separate merged lists into original list & copied list.
while (oldCurr != null) {
oldCurr.next = oldCurr.next.next;
newCurr.next = newCurr.next != null ? newCurr.next.next : null;
oldCurr = oldCurr.next;
newCurr = newCurr.next;
}
}
}
``````
Copy The Code &

Input

cmd

Output

cmd
[[1,1],[2,1]]

### #4 Code Example with Javascript Programming

```Code - Javascript Programming```

``````
return null;
}

// Creating a new weaved list of original and copied nodes.
while (ptr != null) {

// Cloned node
const newNode = new RandomListNode(ptr.label);

A->A'->B->B'->C->C'
newNode.next = ptr.next;
ptr.next = newNode;
ptr = newNode.next;
}

while (ptr != null) {
ptr.next.random = (ptr.random != null) ? ptr.random.next : null;
ptr = ptr.next.next;
}
A'->B'->C'
let ptr_old_list = head; // A->B->C
let ptr_new_list = head.next; // A'->B'->C'
while (ptr_old_list != null) {
ptr_old_list.next = ptr_old_list.next.next;
ptr_new_list.next = (ptr_new_list.next != null) ? ptr_new_list.next.next : null;
ptr_old_list = ptr_old_list.next;
ptr_new_list = ptr_new_list.next;
}
};
``````
Copy The Code &

Input

cmd

Output

cmd
[[1,1],[2,1]]

### #5 Code Example with Python Programming

```Code - Python Programming```

``````
class Solution:
def copyRandomList(self, head: "Node") -> "Node":
dic = collections.defaultdict(lambda: Node(0, None, None))
dic[None] = None
while n:
dic[n].val = n.val
dic[n].next = dic[n.next]
dic[n].random = dic[n.random]
n = n.next
``````
Copy The Code &

Input

cmd

Output

cmd
[[3,null],[3,0],[3,null]]

### #6 Code Example with C# Programming

```Code - C# Programming```

``````
using System.Collections.Generic;

namespace LeetCode
{
public class _0138_CopyListWithRandomPointer
{
{
if (head == null) return null;
var map = new Dictionary < Node, Node>();
while (curr != null)
{
var clone = CloneNode(curr, map);
clone.next = CloneNode(curr.next, map);
clone.random = CloneNode(curr.random, map);

curr = curr.next;
}
}

private Node CloneNode(Node node, IDictionary < Node, Node> map)
{
if (node == null) return null;
if (map.ContainsKey(node)) return map[node];

var clone = new Node(node.val);
map[node] = clone;
return clone;
}

public class Node
{
public int val;
public Node next;
public Node random;

public Node() { }

public Node(int _val)
{
val = _val;
}

public Node(int _val, Node _next, Node _random)
{
val = _val;
next = _next;
random = _random;
}
}
}
}
``````
Copy The Code &

Input

cmd