Flatten a linked list with next and child pointers?

public class MultiLevelNode {
public int val;
public MultiLevelNode next;
public MultiLevelNode child;
public MultiLevelNode(int x) { val = x; next = null; child =

null; }

}

MultiLevelNode Flatten(MultiLevelNode head) {

if (head == null) return null;
MultiLevelNode dummy = new MultiLevelNode(0);
MultiLevelNode prev = dummy;
Stack<MultiLevelNode> stack = new Stack<MultiLevelNode>();

stack.Push(head);

while (stack.Count > 0) {

var curr = stack.Pop();
prev.next = curr;
curr.child = null; // remove child pointer after flattening
prev = curr;
if (curr.next != null) stack.Push(curr.next);
if (curr.child != null) stack.Push(curr.child);
}
return dummy.next;
}

Follow on:

Explanation:

Use a stack to perform DFS; attach nodes and remove child pointers.