[Swift]LeetCode316. 去除重复字母 | Remove Duplicate Letters

概述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 a

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"

给定一个仅包含小写字母的字符串，去除字符串中重复的字母，使得每个字母只出现一次。需保证返回结果的字典序最小（要求不能打乱其他字符的相对位置）。

示例 1:

输入: 输出: "bcabc""abc"

示例 2:

输入: 输出: "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] -= 115             if used[ch,default: false] == true {16                 continue17             }                      18             19             while let last = ans.last,ch < last,counts[last]! > 0 {20                 used[last] = false21                 ans.removeLast()           22             }23             ans.append(ch)24             used[ch] = true25         }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 ans102     }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] = 110             }else {11                 counts[c]! += 112             }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]! -= 126         }27         28         return String(res)29     }30 }

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