#1028
Recover a Tree From Preorder Traversal
hard · verified · 83.2% accepted · 2,289 likes · top 95%
string · tree · depth-first search · binary tree
Description
We run a preorder depth-first search (DFS) on the root of a binary tree.
At each node in this traversal, we output D dashes (where D is the depth of this node), then we output the value of this node. If the depth of a node is D, the depth of its immediate child is D + 1. The depth of the root node is 0.
If a node has only one child, that child is guaranteed to be the left child.
Given the output traversal of this traversal, recover the tree and return its root.
Example 1:
Input: traversal = "1-2--3--4-5--6--7"
Output: [1,2,5,3,4,6,7]
Example 2:
Input: traversal = "1-2--3---4-5--6---7"
Output: [1,2,5,3,null,6,null,4,null,7]
Example 3:
Input: traversal = "1-401--349---90--88"
Output: [1,401,null,349,88,90]
Solution