- Difficulty: Medium
- Tags: LeetCode, Medium, Tree, Depth-First Search, String, Binary Tree, leetcode-606, O(m * n), O(h), Easy, O(n)
Problem
Given the root
node of a binary tree, your task is to create a string representation of the tree following a specific set of formatting rules. The representation should be based on a preorder traversal of the binary tree and must adhere to the following guidelines:
-
Node Representation: Each node in the tree should be represented by its integer value.
-
Parentheses for Children: If a node has at least one child (either left or right), its children should be represented inside parentheses. Specifically:
- If a node has a left child, the value of the left child should be enclosed in parentheses immediately following the node's value.
- If a node has a right child, the value of the right child should also be enclosed in parentheses. The parentheses for the right child should follow those of the left child.
-
Omitting Empty Parentheses: Any empty parentheses pairs (i.e.,
()
) should be omitted from the final string representation of the tree, with one specific exception: when a node has a right child but no left child. In such cases, you must include an empty pair of parentheses to indicate the absence of the left child. This ensures that the one-to-one mapping between the string representation and the original binary tree structure is maintained.In summary, empty parentheses pairs should be omitted when a node has only a left child or no children. However, when a node has a right child but no left child, an empty pair of parentheses must precede the representation of the right child to reflect the tree's structure accurately.
Example 1:
Input: root = [1,2,3,4] Output: "1(2(4))(3)" Explanation: Originally, it needs to be "1(2(4)())(3()())", but you need to omit all the empty parenthesis pairs. And it will be "1(2(4))(3)".
Example 2:
Input: root = [1,2,3,null,4] Output: "1(2()(4))(3)" Explanation: Almost the same as the first example, except the()
after2
is necessary to indicate the absence of a left child for2
and the presence of a right child.
Constraints:
- The number of nodes in the tree is in the range
[1, 104]
. -1000 <= Node.val <= 1000