#988
Smallest String Starting From Leaf
medium · verified · 61.1% accepted · 2,410 likes · top 61%
string · backtracking · tree · depth-first search · binary tree
Description
You are given the root of a binary tree where each node has a value in the range [0, 25] representing the letters 'a' to 'z'.
Return the lexicographically smallest string that starts at a leaf of this tree and ends at the root.
As a reminder, any shorter prefix of a string is lexicographically smaller.
- For example, "ab" is lexicographically smaller than "aba".
A leaf of a node is a node that has no children.
Example 1:
Input: root = [0,1,2,3,4,3,4]
Output: "dba"
Example 2:
Input: root = [25,1,3,1,3,0,2]
Output: "adz"
Example 3:
Input: root = [2,2,1,null,1,0,null,0]
Output: "abc"
Solution