smallest-string-starting-from-leaf

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Algorithms

You are given the <code>root</code> of a binary tree where each node has a value in the range <code>[0, 25]</code> representing the letters <code>&#39;a&#39;</code> to <code>&#39;z&#39;</code>.

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.

<ul>
	<li>For example, <code>&quot;ab&quot;</code> is lexicographically smaller than <code>&quot;aba&quot;</code>.</li>
</ul>

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

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2019/01/30/tree1.png" style="width: 534px; height: 358px;" />
<pre>
Input: root = [0,1,2,3,4,3,4]
Output: &quot;dba&quot;
</pre>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2019/01/30/tree2.png" style="width: 534px; height: 358px;" />
<pre>
Input: root = [25,1,3,1,3,0,2]
Output: &quot;adz&quot;
</pre>

Example 3:
<img alt="" src="https://assets.leetcode.com/uploads/2019/02/01/tree3.png" style="height: 490px; width: 468px;" />
<pre>
Input: root = [2,2,1,null,1,0,null,0]
Output: &quot;abc&quot;
</pre>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 8500]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 25</code></li>
</ul>

smallestFromLeaf

Smallest String Starting From Leaf

Sum Root to Leaf Numbers

sum-root-to-leaf-numbers

求根节点到叶节点数字之和

Binary Tree Paths

binary-tree-paths

二叉树的所有路径

Tree

Depth-First Search

String

Backtracking

Binary Tree

给定一颗根结点为&nbsp;<code>root</code>&nbsp;的二叉树，树中的每一个结点都有一个&nbsp;<code>[0, 25]</code>&nbsp;范围内的值，分别代表字母&nbsp;<code>'a'</code> 到&nbsp;<code>'z'</code>。

返回 按字典序最小 的字符串，该字符串从这棵树的一个叶结点开始，到根结点结束。

<blockquote>
注：字符串中任何较短的前缀在 字典序上 都是 较小 的：

<ul>
	<li>例如，在字典序上&nbsp;<code>"ab"</code> 比&nbsp;<code>"aba"</code>&nbsp;要小。叶结点是指没有子结点的结点。&nbsp;</li>
</ul>
</blockquote>

节点的叶节点是没有子节点的节点。

&nbsp;

<ol>
</ol>

示例 1：

<img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2019/02/02/tree1.png" style="height: 358px; width: 534px;" />

<pre>
输入：root = [0,1,2,3,4,3,4]
输出："dba"
</pre>

示例 2：

<img src="https://assets.leetcode.com/uploads/2019/01/30/tree2.png" />

<pre>
输入：root = [25,1,3,1,3,0,2]
输出："adz"
</pre>

示例 3：

<img src="https://assets.leetcode.com/uploads/2019/02/01/tree3.png" style="height: 513px; width: 490px;" />

<pre>
输入：root = [2,2,1,null,1,0,null,0]
输出："abc"
</pre>

&nbsp;

提示：

<ul>
	<li>给定树的结点数在&nbsp;<code>[1, 8500]</code> 范围内</li>
	<li><code>0 &lt;= Node.val &lt;= 25</code></li>
</ul>