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Problem

Given the root of a binary tree and two integers val and depth, add a row of nodes with value val at the given depth depth.

Note that the root node is at depth 1.

The adding rule is:

Given the integer depth, for each not null tree node cur at the depth depth - 1, create two tree nodes with value val as cur's left subtree root and right subtree root.
cur's original left subtree should be the left subtree of the new left subtree root.
cur's original right subtree should be the right subtree of the new right subtree root.
If depth == 1 that means there is no depth depth - 1 at all, then create a tree node with value val as the new root of the whole original tree, and the original tree is the new root's left subtree.

Examples

Example 1:

80%

Input:
root = [4,2,6,3,1,5], val = 1, depth = 2
Output:
 [4,1,1,2,null,null,6,3,1,5]

Example 2:

80%

Input:
root = [4,2,null,3,1], val = 1, depth = 3
Output:
 [4,2,null,1,1,3,null,null,1]

Solution

Method 1 - DFS

Base case

If the root is null, we do nothing and simply return the root,
If depth is 1, in that case we are adding a new node above current root. So, we should handle that
If depth is 2, we just create 2 tree nodes, with left child being root’s left, and right child being root’s right.
- Then we also update root’s left and right to newly created nodes in respective order
Otherwise, start traversing towards the depth of tree. As, we traverse 1 level lower, we reduce depth by 1

Code

[{"language":"Java","code":"public TreeNode addOneRow(TreeNode root, int val, int depth) {\n\tif (root == null) {\n\t\treturn root;\n\t}\n\tif (depth == 1) {\n\t\treturn new TreeNode(val, root, null);\n\t} else if (depth == 2) {\n\t\troot.left = new TreeNode(val, root.left, null);\n\t\troot.right = new TreeNode(val, null, root.right);\n\t}\n\n\taddOneRow(root.left, val, depth - 1);\n\taddOneRow(root.right, val, depth - 1);\n\t\n\treturn root;\n}","lang":"java"}]

Complexity

Time: O(n) where n is number of nodes in tree.
Space: O(1)

8:["$","div",null,{"className":"max-w-7xl mx-auto px-4 py-8","children":[["$","header",null,{"className":"mb-8 pb-4","children":[["$","div",null,{"className":"flex flex-wrap items-start justify-between gap-4","children":[["$","h1",null,{"className":"text-4xl font-bold text-gray-900 dark:text

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