[Swift]LeetCode1081. 不同字符的最小子序列 | 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: 

Example 2:

Input: 

Example 3:

Input: 

Example 4:

Input:  

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，该子序列包含 text 中所有不同字符一次。

示例 1：

输入："cdadabcc"
输出："adbc"

示例 2：

输入："abcd"
输出："abcd"

示例 3：

输入："ecbacba"
输出："eacb"

示例 4：

输入："leetcode"
输出："letcod" 

提示：

1. 1 <= text.length <= 1000
2. text 由小写英文字母组成

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扩展
28 extension Character
29 {
30     //Character转ASCII整数值(定义小写为整数值)
31     var ascii: Int {
32         get {
33             return Int(self.unicodeScalars.first?.value ?? 0)
34         }
35     }
36 }
37 
38 /*扩展Int类，实现自增++、自减--运算符*/
39 extension Int{
40     //后缀++:先执行表达式后再自增
41     static postfix func ++(num:inout Int) -> Int {
42         //输入输出参数num
43         let temp = num
44         //num加1
45         num += 1
46         //返回加1前的数值
47         return temp
48     }
49 }