Smallest String Starting From Leaf · Interview Problem

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Leetcode

Medium

Trees

Strings

Recursion

Smallest String Starting From Leaf

Build strings from each leaf to the root and return the lexicographically smallest one.

Acceptance 0%

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Problem Statement

Given the root of a binary tree where each node contains a value from 0 to 25, treat the value as a lowercase letter with $0 \to a$ , $1 \to b$ , and so on.

For every leaf node, form a string by reading letters from that leaf up to the root. Among all such strings, return the one that is lexicographically smallest.

A leaf is a node with no children.

Input Format

A binary tree root.
Each node stores an integer in the range $[0, 25]$ .
The tree is provided in the platform's standard tree format.

Output Format

Return a single string: the lexicographically smallest string formed from any leaf to the root.

Constraints

$1 \le$ number of nodes $\le 10^4$
Node values are integers in $[0, 25]$
The tree contains at least one leaf

Examples

Sample cases returned by the problem API.

Example 1

Input

root = [0,1,2,3,4,3,4]

Output

dba

Explanation

The leaf-to-root strings are "dba", "eba", "dca", and "eca". The smallest lexicographically is "dba".

Example 2

Input

root = [25,1,3,1,3,0,2]

Output

adz

Explanation

The leaf-to-root strings include "adz", "bzz", and others. The smallest lexicographically is "adz".

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