Subtree XOR Counting

You are given a tree with $N$ nodes rooted at node $1$. The $i$-th node has a label of $A_i$. A node $v$ is said to be in the **subtree** of $u$ if the simple path from $1$ to $v$ passes through node $u$. We define $S_u$ as the set of all nodes $v$ such that $v \ne u$ and $v$ is in the subtree of $u$. A node $u$ is said to be **good** if either of the following conditions hold: - $S_u$ is empty