[Swift]LeetCode1081. 不一樣字符的最小子序列 | Smallest Subsequence of Distinct Characters

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Return the lexicographically smallest subsequence of text that contains all the distinct characters of textexactly once. 

Example 1:

Input: "cdadabcc"
Output: "adbc" 

Example 2:

Input: "abcd"
Output: "abcd" 

Example 3:

Input: "ecbacba"
Output: "eacb" 

Example 4:

Input: "leetcode"
Output: "letcod" 

Note:

1. 1 <= text.length <= 1000
2. text consists of lowercase English letters.

---

返回字符串 text 中按字典序排列最小的子序列，該子序列包含 text 中全部不一樣字符一次。 

示例 1：

輸入："cdadabcc"
輸出："adbc"

示例 2：

輸入："abcd"
輸出："abcd"

示例 3：

輸入："ecbacba"
輸出："eacb"

示例 4：

輸入："leetcode"
輸出："letcod" 

提示：

1. 1 <= text.length <= 1000
2. text 由小寫英文字母組成

---

12ms

 1 class Solution {
 2 
 3     func smallestSubsequence(_ text: String) -> String {
 4         var cnt = [Int](repeating: 0, count: 26) , used = cnt
 5         var idx = 0, dic = [Character: Int](), chars = Array(text)
 6         _ = "abcdefghijklmnopqrstuvwxyz".map { dic[$0] = idx; idx += 1 }
 7         for ch in chars {
 8             let idx = dic[ch]!
 9             let ct = cnt[idx]
10             cnt[idx] = ct + 1
11         }
12 
13         var ans = ""
14         for ch in chars {
15             let idx = dic[ch]!
16             let ct = cnt[idx]
17             cnt[idx] = ct - 1
18 
19             let uct = used[idx]
20             used[idx] = uct + 1
21             if uct > 0 { continue }
22             while !ans.isEmpty && ans.last! > ch && cnt[dic[ans.last!]!] > 0 {
23                 used[dic[ans.last!]!] = 0
24                 ans.removeLast()
25             }
26             ans += "\(ch)"
27         }
28         return ans
29     }
30 }

---

Runtime: 16 ms

Memory Usage: 21.4 MB

 1 class Solution {
 2     func smallestSubsequence(_ text: String) -> String {
 3         var cnt:[Int] = [Int](repeating:0,count:26)
 4         var used:[Int] = [Int](repeating:0,count:26)
 5         var res:[Character] = [Character]()
 6         let arrText:[Character] = Array(text)
 7         let arrIndex:[Int] = Array(text).map{$0.ascii - 97}
 8         for i in arrIndex
 9         {
10             cnt[i] += 1
11         }
12         for (index,i) in arrIndex.enumerated()
13         {
14             cnt[i] -= 1
15             if used[i]++ > 0 {continue}
16             while(!res.isEmpty && (res.last!.ascii - 97) > i && cnt[res.last!.ascii - 97] > 0)
17             {
18                 used[res.last!.ascii - 97] = 0
19                 res.popLast()
20             }
21             res.append(arrText[index])
22         }
23         return String(res)
24     }
25 }
26 
27 //Character擴展
28 extension Character
29 {
30     //Character轉ASCII整數值(定義小寫爲整數值)
31     var ascii: Int {
32         get {
33             return Int(self.unicodeScalars.first?.value ?? 0)
34         }
35     }
36 }
37 
38 /*擴展Int類，實現自增++、自減--運算符*/
39 extension Int{
40     //後綴++:先執行表達式後再自增
41     static postfix func ++(num:inout Int) -> Int {
42         //輸入輸出參數num
43         let temp = num
44         //num加1
45         num += 1
46         //返回加1前的數值
47         return temp
48     }
49 }