Same Tree Solution

Compare recursively with careful base cases:

function isSameTree(p, q):
    if p == null and q == null:
        return true
    if p == null or q == null:
        return false
    if p.val != q.val:
        return false
    return isSameTree(p.left, q.left) and isSameTree(p.right, q.right)

Three checks:

$1.$ Both null → same (base case)

$2.$ Exactly one null → different

$3.$ Values differ → different

If none of these trigger, recurse on both pairs of children. Both pairs must match.

Time: $O(\min(n, m))$ where $n$ and $m$ are tree sizes.

Space: $O(\min(h_1, h_2))$ for recursion.