https://leetcode.com/problems/clone-graph/?envType=study-plan-v2&envId=top-interview-150
data[Null] * 101
visited[false] * 101
stack = []
stack.push(head)
while stack!=null
node = stack.pop()
if data[node.val] == null
data[node.val] = new Node(node.val)
for (neighbor_node : node.neighbor)
if data[neighbor_node.val] == null
data[neighbor_node.val] = new Node(neighbor_node.val)
data[neight_node.val].neighbor[count++] = neighbor_node
stack.append(neighbor_node)
return data[1]