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Practice Smallest String Starting From Leaf

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#988
LeetCode Problem

Smallest String Starting From Leaf

StringBacktrackingTreeDepth-First SearchBinary Tree

Problem Statement

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. A leaf of a node is a node that has no children.

Source: Smallest String Starting From Leaf on LeetCode. Use the original task for its coding environment and submissions.

Examples

# 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"

Constraints

The number of nodes in the tree is in the range [1, 8500].
0 <= Node.val <= 25

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