leetcode-138-copy-list-with-random-pointer.swift

/**

Copyright (c) 2020 David Seek, LLC

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OR OTHER DEALINGS IN THE SOFTWARE.





https://leetcode.com/problems/copy-list-with-random-pointer/


A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the 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) where random pointer points to, or null if it does not point to any node.
 

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: Given linked list is empty (null pointer), so return null.

*/

/**
Big O Annotation
Time complexity O(n) where n is the amount of nodes in head.
Space complexity O(n) where n is the amount of nodes in head.
*/
func copyRandomList(_ head: Node?) -> Node? {
        
    /**
    Mutable reference of all the nodes 
    to keep track of the random pointers
    */
    var storage: [Node: Node] = [:]

    // Get a copy of the nodes themselves
    let copy = copyNode(head, storage: &storage)

    // And adjust the random pointers
    copyRandom(head, storage: &storage)

    return copy
}

func copyNode(_ node: Node?, storage: inout [Node: Node]) -> Node? {
    
    // Check if there is a node
    guard let node = node else { 
        return nil 
    }
    
    // If so, get a new one with same value
    let copy = Node(node.val)

    // Store the reference for that new node
    storage[node] = copy

    // And continue the recursion down the next elements
    copy.next = copyNode(node.next, storage: &storage)
    
    // Return the new node
    return copy
}

func copyRandom(_ node: Node?, storage: inout [Node: Node]) {

    // Make sure we have a node...    
    guard let node = node else { 
        return 
    }
    
    // Get the random pointer for the current node
    if let random = node.random {

        // And assign it the new one
        storage[node]?.random = storage[random]
    }
    
    // And continue down the recursion 
    copyRandom(node.next, storage: &storage)
}