Subtree of Another Tree

The problem. Given the roots of two binary trees, root and subRoot, return true if some node of root has a subtree that is exactly the same as subRoot — the same structure and values, all the way down to the leaves.

Example

root = [3, 4, 5, 1, 2],  subRoot = [4, 1, 2]                          -> true
root = [3, 4, 5, 1, 2, null, null, null, null, 0],  subRoot = [4, 1, 2] -> false

"Exactly" matters: in the second example, the subtree under 4 has an extra 0 below 2, so it only *contains* subRoot's nodes — it isn't the same tree. A match must also stop where subRoot stops.