623. Add One Row to Tree
Содержание
Use a breadth-first traversal to reach the specific depth, then insert the new nodes. Consider special handling for adding a new root.
To insert a new row, traverse the tree to the specified depth, then adjust the parent-child relationships to include the new nodes. If inserting at depth 1, modify the root directly. Otherwise, modify the children of the nodes at depth d-1.
Approach
- If depth is 1, create a new root and assign the original root as its left child.
- Use a breadth-first search (BFS) to reach level depth-1:
- Use a queue to hold nodes and their current depth.
- For each node at depth d-1, insert new nodes as its left and right children.
- Adjust pointers to connect the new nodes with the subtree of their new children.
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
def addOneRow(root, val, depth):
if depth == 1:
newNode = TreeNode(val)
newNode.left = root
return newNode
queue = [(root, 1)]
while queue:
current, current_depth = queue.pop(0)
if current_depth == depth - 1:
left_child = TreeNode(val, left=current.left, right=None)
right_child = TreeNode(val, left=None, right=current.right)
current.left = left_child
current.right = right_child
else:
if current.left:
queue.append((current.left, current_depth + 1))
if current.right:
queue.append((current.right, current_depth + 1))
return root
class Solution:
def addOneRow(self, root: Optional[TreeNode], val: int, depth: int) -> Optional[TreeNode]:
if depth == 1:
return TreeNode(val, root)
q = deque([root])
i = 0
while q:
i += 1
for _ in range(len(q)):
node = q.popleft()
if node.left:
q.append(node.left)
if node.right:
q.append(node.right)
if i == depth - 1:
node.left = TreeNode(val, node.left, None)
node.right = TreeNode(val, None, node.right)
return root