# 50.第一个只出现一次的字符

### 一、 题目

在字符串 s 中找出第一个只出现一次的字符。如果没有，返回一个单空格。 s 只包含小写字母。

示例 1:

输入：s = "abaccdeff"

输出：'b'

示例 2:

输入：s = ""

输出：' '  

限制：

0 <= s 的长度 <= 50000

来源：力扣（LeetCode）

链接：<https://leetcode-cn.com/problems/di-yi-ge-zhi-chu-xian-yi-ci-de-zi-fu-lcof>

著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

### 二、 解法

```
func firstUniqChar(_ s: String) -> Character {
    let strArr = Array(s)
    var dp: [Character : Int] = [:]
    var indexs: [Character] = []
    
    strArr.forEach {
        if dp[$0] != nil {
            if let idx = indexs.firstIndex(of: $0) {
                indexs.remove(at: idx)                
            }
        }
        else {
            dp[$0] = 1
            indexs.append($0)
        }
    }
    
    return indexs.first ?? " "
}
```


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