Question

138. Copy List with Random Pointer

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Description

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.

Return _the head of the copied linked list_.

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.

Solutions

Solution 1

"""
# Definition for a Node.
class Node:
  def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):
    self.val = int(x)
    self.next = next
    self.random = random
"""


class Solution:
  def copyRandomList(self, head: "Node") -> "Node":
    d = {}
    dummy = tail = Node(0)
    cur = head
    while cur:
      tail.next = Node(cur.val)
      tail = tail.next
      d[cur] = tail
      cur = cur.next
    tail = dummy.next
    cur = head
    while cur:
      tail.random = d.get(cur.random)
      tail = tail.next
      cur = cur.next
    return dummy.next

/*
// Definition for a Node.
class Node {
  int val;
  Node next;
  Node random;

  public Node(int val) {
    this.val = val;
    this.next = null;
    this.random = null;
  }
}
*/
class Solution {
  public Node copyRandomList(Node head) {
    Map<Node, Node> d = new HashMap<>();
    Node dummy = new Node(0);
    Node tail = dummy;
    for (Node cur = head; cur != null; cur = cur.next) {
      tail.next = new Node(cur.val);
      tail = tail.next;
      d.put(cur, tail);
    }
    tail = dummy.next;
    for (Node cur = head; cur != null; cur = cur.next) {
      tail.random = d.get(cur.random);
      tail = tail.next;
    }
    return dummy.next;
  }
}

/*
// Definition for a Node.
class Node {
public:
  int val;
  Node* next;
  Node* random;

  Node(int _val) {
    val = _val;
    next = NULL;
    random = NULL;
  }
};
*/
class Solution {
public:
  Node* copyRandomList(Node* head) {
    unordered_map<Node*, Node*> d;
    Node* dummy = new Node(0);
    Node* tail = dummy;
    for (auto cur = head; cur; cur = cur->next) {
      tail->next = new Node(cur->val);
      tail = tail->next;
      d[cur] = tail;
    }
    tail = dummy->next;
    for (auto cur = head; cur; cur = cur->next) {
      tail->random = d[cur->random];
      tail = tail->next;
    }
    return dummy->next;
  }
};

/**
 * Definition for a Node.
 * type Node struct {
 *   Val int
 *   Next *Node
 *   Random *Node
 * }
 */

func copyRandomList(head *Node) *Node {
  d := map[*Node]*Node{}
  dummy := &Node{}
  tail := dummy
  for cur := head; cur != nil; cur = cur.Next {
    tail.Next = &Node{Val: cur.Val}
    tail = tail.Next
    d[cur] = tail
  }
  tail = dummy.Next
  for cur := head; cur != nil; cur = cur.Next {
    tail.Random = d[cur.Random]
    tail = tail.Next
  }
  return dummy.Next
}

/**
 * Definition for Node.
 * class Node {
 *   val: number
 *   next: Node | null
 *   random: Node | null
 *   constructor(val?: number, next?: Node, random?: Node) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 *     this.random = (random===undefined ? null : random)
 *   }
 * }
 */

function copyRandomList(head: Node | null): Node | null {
  const map = new Map<Node, Node>();
  let cur = head;
  while (cur != null) {
    map.set(cur, new Node(cur.val));
    cur = cur.next;
  }
  cur = head;
  while (cur != null) {
    map.get(cur).next = map.get(cur.next) ?? null;
    map.get(cur).random = map.get(cur.random) ?? null;
    cur = cur.next;
  }
  return map.get(head);
}

/**
 * // Definition for a Node.
 * function Node(val, next, random) {
 *  this.val = val;
 *  this.next = next;
 *  this.random = random;
 * };
 */

/**
 * @param {Node} head
 * @return {Node}
 */
var copyRandomList = function (head) {
  const d = new Map();
  const dummy = new Node(0);
  let tail = dummy;
  for (let cur = head; cur; cur = cur.next) {
    tail.next = new Node(cur.val);
    tail = tail.next;
    d.set(cur, tail);
  }
  tail = dummy.next;
  for (let cur = head; cur; cur = cur.next) {
    tail.random = d.get(cur.random);
    tail = tail.next;
  }
  return dummy.next;
};

/*
// Definition for a Node.
public class Node {
  public int val;
  public Node next;
  public Node random;

  public Node(int _val) {
    val = _val;
    next = null;
    random = null;
  }
}
*/

public class Solution {
  public Node CopyRandomList(Node head) {
    Dictionary<Node, Node> d = new Dictionary<Node, Node>();
    Node dummy = new Node(0);
    Node tail = dummy;
    for (Node cur = head; cur != null; cur = cur.next) {
      tail.next = new Node(cur.val);
      tail = tail.next;
      d[cur] = tail;
    }
    tail = dummy.next;
    for (Node cur = head; cur != null; cur = cur.next) {
      tail.random = cur.random == null ? null : d[cur.random];
      tail = tail.next;
    }
    return dummy.next;
  }
}

Solution 2

"""
# Definition for a Node.
class Node:
  def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):
    self.val = int(x)
    self.next = next
    self.random = random
"""


class Solution:
  def copyRandomList(self, head: "Node") -> "Node":
    if head is None:
      return None
    cur = head
    while cur:
      node = Node(cur.val, cur.next)
      cur.next = node
      cur = node.next

    cur = head
    while cur:
      if cur.random:
        cur.next.random = cur.random.next
      cur = cur.next.next

    ans = head.next
    cur = head
    while cur:
      nxt = cur.next
      if nxt:
        cur.next = nxt.next
      cur = nxt
    return ans

/*
// Definition for a Node.
class Node {
  int val;
  Node next;
  Node random;

  public Node(int val) {
    this.val = val;
    this.next = null;
    this.random = null;
  }
}
*/
class Solution {
  public Node copyRandomList(Node head) {
    if (head == null) {
      return null;
    }
    for (Node cur = head; cur != null;) {
      Node node = new Node(cur.val, cur.next);
      cur.next = node;
      cur = node.next;
    }
    for (Node cur = head; cur != null; cur = cur.next.next) {
      if (cur.random != null) {
        cur.next.random = cur.random.next;
      }
    }
    Node ans = head.next;
    for (Node cur = head; cur != null;) {
      Node nxt = cur.next;
      if (nxt != null) {
        cur.next = nxt.next;
      }
      cur = nxt;
    }
    return ans;
  }
}

/*
// Definition for a Node.
class Node {
public:
  int val;
  Node* next;
  Node* random;

  Node(int _val) {
    val = _val;
    next = NULL;
    random = NULL;
  }
};
*/
class Solution {
public:
  Node* copyRandomList(Node* head) {
    if (!head) {
      return nullptr;
    }
    for (Node* cur = head; cur;) {
      Node* node = new Node(cur->val);
      node->next = cur->next;
      cur->next = node;
      cur = node->next;
    }
    for (Node* cur = head; cur; cur = cur->next->next) {
      if (cur->random) {
        cur->next->random = cur->random->next;
      }
    }
    Node* ans = head->next;
    for (Node* cur = head; cur;) {
      Node* nxt = cur->next;
      if (nxt) {
        cur->next = nxt->next;
      }
      cur = nxt;
    }
    return ans;
  }
};

/**
 * Definition for a Node.
 * type Node struct {
 *   Val int
 *   Next *Node
 *   Random *Node
 * }
 */

func copyRandomList(head *Node) *Node {
  if head == nil {
    return nil
  }
  for cur := head; cur != nil; {
    node := &Node{cur.Val, cur.Next, nil}
    cur.Next = node
    cur = node.Next
  }
  for cur := head; cur != nil; cur = cur.Next.Next {
    if cur.Random != nil {
      cur.Next.Random = cur.Random.Next
    }
  }
  ans := head.Next
  for cur := head; cur != nil; {
    nxt := cur.Next
    if nxt != nil {
      cur.Next = nxt.Next
    }
    cur = nxt
  }
  return ans
}

/**
 * // Definition for a Node.
 * function Node(val, next, random) {
 *  this.val = val;
 *  this.next = next;
 *  this.random = random;
 * };
 */

/**
 * @param {Node} head
 * @return {Node}
 */
var copyRandomList = function (head) {
  if (!head) {
    return null;
  }
  for (let cur = head; cur; ) {
    const node = new Node(cur.val, cur.next, null);
    cur.next = node;
    cur = node.next;
  }
  for (let cur = head; cur; cur = cur.next.next) {
    if (cur.random) {
      cur.next.random = cur.random.next;
    }
  }
  const ans = head.next;
  for (let cur = head; cur; ) {
    const nxt = cur.next;
    if (nxt) {
      cur.next = nxt.next;
    }
    cur = nxt;
  }
  return ans;
};

/*
// Definition for a Node.
public class Node {
  public int val;
  public Node next;
  public Node random;

  public Node(int _val) {
    val = _val;
    next = null;
    random = null;
  }
}
*/

public class Solution {
  public Node CopyRandomList(Node head) {
    if (head == null) {
      return null;
    }
    for (Node cur = head; cur != null; ) {
      Node node = new Node(cur.val, cur.next);
      cur.next = node;
      cur = node.next;
    }
    for (Node cur = head; cur != null; cur = cur.next.next) {
      if (cur.random != null) {
        cur.next.random = cur.random.next;
      }
    }
    Node ans = head.next;
    for (Node cur = head; cur != null; ) {
      Node nxt = cur.next;
      if (nxt != null) {
        cur.next = nxt.next;
      }
      cur = nxt;
    }
    return ans;
  }
}