100. 相同的树

输入:       1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

输出: true

输入:      1          1
          /           \
         2             2

        [1,2],     [1,null,2]

输出: false

输入:       1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

输出: false

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func isSameTree(p *TreeNode, q *TreeNode) bool {
	if p == nil && q == nil {
		return true
	} else if p == nil || q == nil {
		return false
	}

	if p.Val != q.Val {
		return false
	}

	return isSameTree(p.Left, q.Left) && isSameTree(p.Right, q.Right)
}