判斷兩棵樹是否相同

func isSameTree(p *TreeNode, q *TreeNode) bool {

    if p == nil && q == nil {
        return true
    }
    if (p == nil && q != nil) || (p != nil && q == nil) {
        return false
    }
    if p.Val != q.Val {
        return false
    }
    return isSameTree(p.Left, q.Left) && isSameTree(p.Right, q.Right)
}