[Day32-02]-[二叉树] 在二叉树中增加一行

输入: root = [4,2,6,3,1,5], val = 1, depth = 2输出: [4,1,1,2,null,null,6,3,1,5]

输入: root = [4,2,null,3,1], val = 1, depth = 3输出:  [4,2,null,1,1,3,null,null,1]

func TestAddOneRow(t *testing.T) {	root := &TreeNode{		Val: 1,		Left: &TreeNode{			Val: 2,			Left: &TreeNode{				Val: 4,			},		},		Right: &TreeNode{			Val: 3,		},	}	// 题解：
	var depth = 3                          // 插入的层级	var val = 5                            // 新节点的val	var dfs func(root *TreeNode, curr int) // 递归 DLR	dfs = func(root *TreeNode, curr int) {		if root == nil { // 递归终止条件			return		}		if curr == depth-1 {			l := root.Left         // 临时存储左节点			r := root.Right        // 临时存储右节点			root.Left = &TreeNode{ // 新节点				Val:  val,				Left: l,			}			root.Right = &TreeNode{ // 新节点				Val:   val,				Right: r,			}		}		dfs(root.Left, curr+1)		dfs(root.Right, curr+1)	}
	solution := func(root *TreeNode) *TreeNode {		if depth == 1 { // 特殊兼容depth=1的情况			return &TreeNode{				Val:  val,				Left: root,			}		}		dfs(root, 1)		return root	}
	t.Log(solution(root))}