[Swift]LeetCode316. 去除重複字母 | Remove Duplicate Letters

★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★
➤微信公衆號：山青詠芝（shanqingyongzhi）
➤博客園地址：山青詠芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：http://www.javashuo.com/article/p-mepohdnx-kn.html 
➤若是連接不是山青詠芝的博客園地址，則多是爬取做者的文章。
➤原文已修改更新！強烈建議點擊原文地址閱讀！支持做者！支持原創！
★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★★

Given a string which contains only lowercase letters, remove duplicate letters so that every letter appear once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.

Example 1:

Input: 
Output: 
"bcabc""abc"

Example 2:

Input: 
Output: "cbacdcbc""acdb"

---

給定一個僅包含小寫字母的字符串，去除字符串中重複的字母，使得每一個字母只出現一次。需保證返回結果的字典序最小（要求不能打亂其餘字符的相對位置）。

示例 1:

輸入: 
輸出: 
"bcabc""abc"

示例 2:

輸入: 
輸出: "cbacdcbc""acdb"

---

32ms

 1 class Solution {
 2     func removeDuplicateLetters(_ s: String) -> String {
 3         
 4         var counts = [Character: Int]()
 5         var used = [Character:Bool]()
 6         
 7         s.forEach {
 8             counts[$0, default: 0] += 1
 9         }
10         
11         var ans = [Character]()
12         
13         for ch in s {
14             counts[ch, default:0] -= 1
15             if used[ch, default: false] == true {
16                 continue
17             }                      
18             
19             while let last = ans.last, ch < last, counts[last]! > 0 {
20                 used[last] = false
21                 ans.removeLast()           
22             }
23             ans.append(ch)
24             used[ch] = true
25         }
26 
27         return String(ans)
28     }
29 }

---

36ms

  1 extension Character {
  2     var ascii: UInt32? {   
  3         guard let first = unicodeScalars.first else {
  4             return nil
  5         }
  6         return first.isASCII == true ? first.value : nil    
  7     }
  8 }
  9 
 10 class Solution {
 11     class IndexedTree {
 12         var n: Int
 13         var arr: [Int]
 14         
 15         init(_ n: Int) {
 16             self.n = n
 17             arr = [Int](repeating: 0, count: n+1)
 18         }
 19         
 20         func insert(_ index: Int) -> Void {
 21             var x = index
 22             while x <= n {
 23                 arr[x] += 1
 24                 x = x + x&(-x)
 25             }
 26         }
 27         
 28         func query(_ index: Int) -> Int {
 29             var x = index
 30             var sum = 0
 31             while x > 0 {
 32                 sum += arr[x]
 33                 x = x&(x-1)
 34             }
 35             return sum
 36         }
 37     }
 38     
 39 
 40     func transIndex(_ n: Int, _ index: Int) -> Int {
 41         return n-index
 42     }
 43     
 44     func removeDuplicateLetters(_ s: String) -> String {
 45         let charArr = Array(s)
 46         var ans = ""
 47         
 48         let n = charArr.count
 49         if n == 0 {
 50             return ans
 51         }
 52         
 53         var counts = [Int](repeating: 0, count: 26)
 54         var indice = [Int?](repeating: nil, count: 26)
 55         var used = [Bool](repeating: false, count: 26)
 56         
 57         let indexedTree = IndexedTree(charArr.count)
 58         let aAsc = "a".first!.ascii!
 59         
 60         for (i, ch) in charArr.enumerated(){
 61             let ci = Int(ch.ascii!-aAsc)
 62             counts[ci] += 1
 63         }
 64         
 65         var que = [Int]()
 66         for (i, ch) in charArr.enumerated() {
 67             let ci = Int(ch.ascii!-aAsc)
 68             if counts[ci] == 0 {
 69                 continue
 70             }
 71 
 72 
 73             
 74             if indice[ci] == nil {
 75                 while let last = que.last {
 76                     if last > ci {
 77                         que.removeLast()
 78                         indice[last] = nil
 79                     } else {
 80                         break
 81                     }
 82                 }
 83                 
 84                 indice[ci] = i
 85                 que.append(ci)
 86             }
 87             
 88             counts[ci] -= 1
 89             if counts[ci] == 0 {
 90                 while let ii = que.first, ii <= ci {
 91                     let index = indice[ii]!
 92                     ans += String(charArr[index])
 93                     indice[ii] = nil
 94                     counts[ii] = 0
 95                     que.removeFirst()
 96                 }
 97             }
 98 
 99         }
100     
101         return ans
102     }
103 }

---

52ms

 1 class Solution {
 2     func removeDuplicateLetters(_ s: String) -> String {
 3         let sArr = Array(s)
 4         
 5         var counts = [Character : Int]()
 6         
 7         for c in sArr {
 8             if counts[c] == nil {
 9                 counts[c] = 1
10             }else {
11                 counts[c]! += 1
12             }
13         }
14         
15         var res = [Character]()
16         
17         for c in sArr {
18             if !res.contains(c) {
19                 while !res.isEmpty && counts[res.last!] != 0 && res.last! > c  {
20                     res.removeLast()
21                 }
22                 res.append(c)
23                 
24             }
25             counts[c]! -= 1
26         }
27         
28         return String(res)
29     }
30 }