first-unique-character-in-a-string

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python3

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Algorithms

Given a string <code>s</code>, find the first non-repeating character in it and return its index. If it does not exist, return <code>-1</code>.

&nbsp;
Example 1:

<div class="example-block">
Input: s = &quot;leetcode&quot;

Output: 0

Explanation:

The character <code>&#39;l&#39;</code> at index 0 is the first character that does not occur at any other index.
</div>

Example 2:

<div class="example-block">
Input: s = &quot;loveleetcode&quot;

Output: 2
</div>

Example 3:

<div class="example-block">
Input: s = &quot;aabb&quot;

Output: -1
</div>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
</ul>

firstUniqChar

First Unique Character in a String

Sort Characters By Frequency

sort-characters-by-frequency

根据字符出现频率排序

First Letter to Appear Twice

first-letter-to-appear-twice

第一个出现两次的字母

Queue

Hash Table

String

Counting

给定一个字符串&nbsp;<code>s</code>&nbsp;，找到 它的第一个不重复的字符，并返回它的索引 。如果不存在，则返回 <code>-1</code>&nbsp;。

&nbsp;

示例 1：

<pre>
输入: s = "leetcode"
输出: 0
</pre>

示例 2:

<pre>
输入: s = "loveleetcode"
输出: 2
</pre>

示例 3:

<pre>
输入: s = "aabb"
输出: -1
</pre>

&nbsp;

提示:

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s</code>&nbsp;只包含小写字母</li>
</ul>