Question
Given a linked list where each node has two pointers, one to the next node and one to a random node in the list, clone the linked list.
eg.
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1 2 3 4 |
1 -> 2 -> 3 -> 4 -> null | | | | v v v v 3 1 3 2 |
Once you think that you’ve solved the problem, click below to see the solution.
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Solution
How was that problem? You can check out the solution in the video below.
Here is the source code for the solution shown in the video (Github):
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// Private node class private static class Node { int value; Node next; Node random; } // Copy list using extra space. Store mapping of old nodes to new nodes public static Node cloneExtraSpace(Node n) { if (n == null) return n; // Map nodes in old list to equivalent nodes in new list HashMap<Node, Node> mapping = new HashMap<Node, Node>(); // Create new linked list, minus the random node pointers. Save mapping // of equivalent old node to new node Node copy = new Node(); Node nCurr = n, copyCurr = copy; mapping.put(nCurr, copyCurr); while (nCurr.next != null) { copyCurr.next = new Node(); nCurr = nCurr.next; copyCurr = copyCurr.next; mapping.put(nCurr, copyCurr); } // Copy the random pointers. Find the random pointer in the original // list and look up the equivalent using the map nCurr = n; copyCurr = copy; while (nCurr != null) { copyCurr.random = mapping.get(nCurr.random); nCurr = nCurr.next; copyCurr = copyCurr.next; } return copy; } // Copy list without using extra space. Interleave the nodes from the new // with the nodes from the original list. Then separate the new list from // the old public static Node cloneNoExtraSpace(Node n) { if (n == null) return n; // Create new nodes in between the original nodes Node nCurr = n; while (nCurr != null) { Node temp = new Node(); temp.value = nCurr.value; temp.next = nCurr.next; nCurr.next = temp; nCurr = nCurr.next.next; } // Copy random pointers nCurr = n; while (nCurr != null) { nCurr.next.random = nCurr.random.next; nCurr = nCurr.next.next; } // Separate new nodes from old nodes Node copy = n.next; nCurr = n; while (nCurr.next != null) { Node tmp = nCurr.next; nCurr.next = nCurr.next.next; nCurr = tmp; } return copy; } |
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