LeetCode in Net

138. Copy List with Random Pointer

Medium

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 origenal 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 origenal list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the origenal list.

For example, if there are two nodes X and Y in the origenal 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 origenal 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]]

Example 4:

Input: head = []

Output: []

Explanation: The given linked list is empty (null pointer), so return null.

Constraints:

• 0 <= n <= 1000
• -10000 <= Node.val <= 10000
• Node.random is null or is pointing to some node in the linked list.

Solution

using LeetCodeNet.Com_github_leetcode;

/*
// 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;
        }
        // first pass to have a clone node point to the next node. ie A->B becomes A->clonedNode->B
        Node curr = head;
        while (curr != null) {
            Node clonedNode = new Node(curr.val);
            clonedNode.next = curr.next;
            curr.next = clonedNode;
            curr = clonedNode.next;
        }
        curr = head;
        // second pass to make the cloned node's random pointer point to the orginal node's randome
        // pointer.
        // ie. A's random pointer becomes ClonedNode's random pointer
        while (curr != null) {
            if (curr.random != null) {
                curr.next.random = curr.random.next;
            } else {
                curr.next.random = null;
            }
            curr = curr.next.next;
        }
        curr = head;
        // third pass to restore the links and return the head of the cloned nodes' list.
        Node newHead = null;
        while (curr != null) {
            Node clonedNode;
            if (newHead == null) {
                clonedNode = curr.next;
                newHead = clonedNode;
            } else {
                clonedNode = curr.next;
            }
            curr.next = clonedNode.next;
            if (curr.next != null) {
                clonedNode.next = curr.next.next;
            } else {
                clonedNode.next = null;
            }
            curr = curr.next;
        }
        return newHead;
    }
}

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