[Swift]LeetCode387. 字符串中的第一个惟一字符 | First Unique Character in a String

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Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

 

Note: You may assume the string contain only lowercase letters.

给定一个字符串，找到它的第一个不重复的字符，并返回它的索引。若是不存在，则返回 -1。

案例:

s = "leetcode"
返回 0.

s = "loveleetcode",
返回 2.

 

注意事项：您能够假定该字符串只包含小写字母。

---

 1 class Solution {
 2     func firstUniqChar(_ s: String) -> Int {
 3        //把英文字符都存入数组中
 4         var arr = Array<Int>(repeating: 0, count: 26)
 5         for asc in s.unicodeScalars
 6         {
 7             let num:Int = Int(asc.value - 97)
 8             //记录字符出现的次数
 9             arr[num] += 1
10         }
11         //再次循环字符串，使用enumerated()获取到字符串的索引
12         for (index, asc) in s.unicodeScalars.enumerated()
13         {
14             let count = arr[Int(asc.value - 97)]
15             if count == 1 {
16                 return index
17             }
18         }
19         return -1
20     }
21 }

---

104ms

 1 class Solution {
 2     func firstUniqChar(_ s: String) -> Int {
 3         var list:[Int] = [Int](repeating: 0, count: 26)
 4         for charCode in s.unicodeScalars {
 5             let tempIndex:Int = Int(charCode.value) - 97
 6             list[tempIndex] += 1
 7         }
 8         
 9         var index = 0
10         for charCode in s.unicodeScalars {
11             let tempIndex:Int = Int(charCode.value) - 97
12             if list[tempIndex] == 1 {
13                 return index
14             }
15             index += 1
16         }
17         return -1
18     }
19 }

---

128ms

 1 class Solution {
 2   func firstUniqChar(_ s: String) -> Int {
 3       var countFor = Array(repeating:0, count:26)
 4       let offset = 97
 5       for charCode in s.utf8 {
 6           let adjustedCharCode = Int(charCode) - offset
 7           countFor[adjustedCharCode] += 1
 8       }
 9       for (i, charCode) in s.utf8.enumerated() {
10           let adjustedCharCode = Int(charCode) - offset
11           if countFor[adjustedCharCode] == 1 {
12               return i
13           }
14       }
15       return -1
16   }
17 }