cloneGraph.kt

/**
 * Definition for a Node.
 * class Node(var `val`: Int) {
 *     var neighbors: ArrayList<Node?> = ArrayList<Node?>()
 * }
 */

class Solution {
    fun cloneGraph(node: Node?): Node? {
        return cloneGraph(node, mutableMapOf())
    }

    fun cloneGraph(node: Node?, m: MutableMap<Int, Node>): Node? {
        if (node == null) { return null }
        if (m[node.`val`] != null) { return m[node.`val`] }

        val newNode = Node(node.`val`)
        m[node.`val`] = newNode
        newNode.neighbors = ArrayList(node.neighbors
            .toList()
            .filter { it != null }
            .map { cloneGraph(it, m) })
        
        return newNode
    }
}