All Elements in Two Binary Search Trees
<p>Given two binary search trees <code>root1</code> and <code>root2</code>, return <em>a list containing all the integers from both trees sorted in <strong>ascending</strong> order</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1300-1399/1305.All%20Elements%20in%20Two%20Binary%20Search%20Trees/images/q2-e1.png" style="width: 457px; height: 207px;" />
<pre>
<strong>Input:</strong> root1 = [2,1,4], root2 = [1,0,3]
<strong>Output:</strong> [0,1,1,2,3,4]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1300-1399/1305.All%20Elements%20in%20Two%20Binary%20Search%20Trees/images/q2-e5-.png" style="width: 352px; height: 197px;" />
<pre>
<strong>Input:</strong> root1 = [1,null,8], root2 = [8,1]
<strong>Output:</strong> [1,1,8,8]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in each tree is in the range <code>[0, 5000]</code>.</li>
	<li><code>-10<sup>5</sup> &lt;= Node.val &lt;= 10<sup>5</sup></code></li>
</ul>
Tree; Depth-First Search; Binary Search Tree; Binary Tree; Sorting
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func getAllElements(root1 *TreeNode, root2 *TreeNode) (ans []int) {
	var dfs func(*TreeNode, *[]int)
	dfs = func(root *TreeNode, nums *[]int) {
		if root == nil {
			return
		}
		dfs(root.Left, nums)
		*nums = append(*nums, root.Val)
		dfs(root.Right, nums)
	}
	a, b := []int{}, []int{}
	dfs(root1, &a)
	dfs(root2, &b)
	i, j := 0, 0
	m, n := len(a), len(b)
	for i < m && j < n {
		if a[i] < b[j] {
			ans = append(ans, a[i])
			i++
		} else {
			ans = append(ans, b[j])
			j++
		}
	}
	for ; i < m; i++ {
		ans = append(ans, a[i])
	}
	for ; j < n; j++ {
		ans = append(ans, b[j])
	}
	return
}
