[Swift]LeetCode394. 字符串解码 | Decode String

原文地址：https://www.cnblogs.com/strengthen/p/10300572.html

Given an encoded string, return it's decoded string.

The encoding rule is: k[encoded_string], where the encoded_stringinside the square brackets is being repeated exactly k times. Note that kis guaranteed to be a positive integer.

You may assume that the input string is always valid; No extra white spaces, square brackets are well-formed, etc.

Furthermore, you may assume that the original data does not contain any digits and that digits are only for those repeat numbers, k. For example, there won't be input like 3a or 2[4].

Examples:

s = "3[a]2[bc]", return "aaabcbc".
s = "3[a2[c]]", return "accaccacc".
s = "2[abc]3[cd]ef", return "abcabccdcdcdef".

给定一个经过编码的字符串，返回它解码后的字符串。

编码规则为: k[encoded_string]，表示其中方括号内部的 encoded_string 正好重复 k 次。注意 k 保证为正整数。

你可以认为输入字符串总是有效的；输入字符串中没有额外的空格，且输入的方括号总是符合格式要求的。

此外，你可以认为原始数据不包含数字，所有的数字只表示重复的次数 k，例如不会出现像 3a 或 2[4] 的输入。

示例:

s = "3[a]2[bc]", 返回 "aaabcbc".
s = "3[a2[c]]", 返回 "accaccacc".
s = "2[abc]3[cd]ef", 返回 "abcabccdcdcdef".

12ms

 1 class Solution {
 2     func decodeString(_ s: String) -> String {
 3         var k:Int = 0
 4         return DFS(s, &k)        
 5     }
 6     
 7     func DFS(_ s:String,_ k:inout Int) -> String
 8     {
 9         var ans:String = String()
10         var cnt:Int = 0
11         while(k < s.count)
12         {
13             if s[k] >= "0" && s[k] <= "9"
14             {
15                 cnt = cnt*10 + (s[k].ascii - 48)
16                 k += 1
17             }
18             else if s[k] == "["
19             {
20                 k += 1
21                 var tem:String = DFS(s, &k)
22                 for i in 0..<cnt
23                 {
24                     ans += tem
25                     cnt = 0
26                 }
27             }
28             else if s[k] == "]"
29             {
30                 k += 1
31                 return ans
32             }
33             else
34             {
35                 ans.append(s[k])
36                 k += 1
37             }
38         }
39         return ans        
40     }
41 }
42 
43 extension String {        
44     //subscript函数可以检索数组中的值
45     //直接按照索引方式截取指定索引的字符
46     subscript (_ i: Int) -> Character {
47         //读取字符
48         get {return self[index(startIndex, offsetBy: i)]}
49     }
50 }
51 
52 //Character扩展方法  
53 extension Character  
54 {  
55   //属性：ASCII整数值(定义小写为整数值)
56    var ascii: Int {
57         get {
58             let s = String(self).unicodeScalars
59             return Int(s[s.startIndex].value)
60         }
61     }
62 }

12ms

 1 class Solution {
 2     func decodeString(_ s: String) -> String {
 3         var i = 0
 4         return String(de(Array(s),&i))
 5     }
 6     
 7     let zv = "0".unicodeScalars.first!.value, nv = "9".unicodeScalars.first!.value
 8     
 9     func de(_ c: [Character], _ i: inout Int) -> [Character]{
10         var num = 0
11         var ans = [Character]()
12         while i < c.count && c[i] != "]" {
13             let iv = c[i].unicodeScalars.first!.value
14             if iv<=nv && iv>=zv {
15                 num = num*10 + Int(iv-zv)
16             } else if c[i] == "[" {
17                 i+=1
18                 let re = de(c, &i)
19                 for j in  0..<num {
20                     ans += re
21                 }
22                 num=0
23                 
24             } else {
25                 ans.append(c[i])
26             }
27             i+=1
28         }
29         return ans
30     }
31 }

12ms

 1 import Foundation
 2 class Solution {
 3     func decodeString(_ s: String) -> String {
 4     var numOfLeft:Int = 0;
 5     var tempStack:[Character] = [Character]();
 6     var resultString:String = String();
 7     
 8     func toStringWhenRight()->String{//遇到不是数字就停止
 9         var tempStr = ""
10         var tempNum = ""
11         var result = ""
12         while tempStack[tempStack.count-1] != "[" {
13             let temp = String.init(tempStack.popLast()!)
14             tempStr = temp + tempStr;
15         }
16         tempStack.removeLast()
17         while (tempStack.count>0&&tempStack[tempStack.count-1]>="0"&&tempStack[tempStack.count-1]<="9"){
18             let temp = String.init(tempStack.popLast()!)
19             tempNum = temp + tempNum;
20             // print(tempStack.count)
21         }
22         let bound = (tempNum as NSString).integerValue
23         for _ in 1...bound{
24             result += tempStr
25         }
26         //读取其余的字母
27         while (tempStack.count>0&&tempStack[tempStack.count-1]>="a"&&tempStack[tempStack.count-1]<="z"){
28             let str = String.init(tempStack.popLast()!)
29             result =  str + result;
30         }
31         numOfLeft -= 1;
32         return result
33     }
34     for char in s{
35         if(char == "["){
36             numOfLeft+=1;
37             tempStack.append(char);
38         }else if(char=="]"){
39             if(numOfLeft == 1){
40                 resultString += toStringWhenRight();
41             }else if(numOfLeft > 1){
42                 tempStack.append(contentsOf: toStringWhenRight());
43             }else{fatalError("something strange hanppens")}
44         }else{
45             tempStack.append(char);
46         }
47     }
48     resultString += String.init(tempStack);
49     return resultString;
50   }
51 }

16ms

  1 class Solution {
  2    
  3     func decodeString(_ str: String) -> String {
  4         // stores the ascii values of the characters
  5         var stack: [String] = []
  6 
  7         // used to store the formed number of times
  8         var number: Int? = 0
  9 
 10         // running index in str
 11         var index = 0
 12         while index < str.count {
 13             let ch = str[index]
 14 
 15             if ch.isNumeric() {
 16                 number = (number ?? 0) * 10 + ch.numericValue()!
 17             } else if ch == "[" {
 18                 if let number = number {
 19                     stack.append(String(number))
 20                 }
 21                 number = nil
 22                 stack.append(String(ch))
 23             } else if ch == "]" {
 24                 number = nil
 25                 // decode the string and push on to stack
 26                 var values = [String]()
 27                 var times = 0
 28                 while let top = stack.last {
 29                     if top == "[" {
 30                         // removes the square bracket
 31                         stack.removeLast()
 32 
 33                         // remove the number
 34                         times = Int(stack.removeLast())!
 35 
 36                         break
 37                     } else {
 38                         values.insert(stack.removeLast(), at: 0)
 39                     }
 40                 }
 41 
 42                 stack.append(decodeString(times, values))
 43             } else {
 44                 number = nil
 45                 // any other character
 46                 stack.append(String(ch))
 47             }
 48 
 49             index += 1
 50         }
 51 
 52         let result = stack.reduce("") { $0 + $1 }
 53         return result
 54     }
 55 
 56     func decodeString(_ times: Int, _ values: [String]) -> String {
 57         let str = values.reduce("", +)
 58         var result = ""
 59         for _ in 0..<times {
 60             result += str
 61         }
 62 
 63         return result
 64     }
 65         
 66 }
 67         
 68 extension String {
 69     
 70     subscript (i: Int) -> Character {
 71         return self[index(startIndex, offsetBy: i)]
 72     }
 73     
 74     func subString(from: Int, to: Int) -> String {
 75         guard from <= to else {
 76             return ""
 77         }
 78         
 79         let startIndex = self.index(self.startIndex, offsetBy: from)
 80         let endIndex = self.index(self.startIndex, offsetBy: to)
 81         return String(self[startIndex...endIndex])
 82     }
 83     
 84     func subString(from: Int) -> String {
 85         let startIndex = self.index(self.startIndex, offsetBy: from)
 86         return String(self.suffix(from: startIndex))
 87     }
 88     
 89     func asciiValues() -> [Int] {
 90         return Array(self.utf16).map { Int($0) }
 91     }
 92     
 93     mutating func lTrim() {
 94         if let trailingSpacesRange = self.range(of: "^\s+", options: .regularExpression) {
 95             self.replaceSubrange(trailingSpacesRange, with: "")
 96         }
 97     }
 98     
 99     mutating func rTrim() {
100         if let trailingSpacesRange = self.range(of: "\s+$", options: .regularExpression) {
101             self.replaceSubrange(trailingSpacesRange, with: "")
102         }
103     }
104     
105 }
106 
107 struct AsciiValue {
108     static let zero = Int(Character("0").unicodeScalars.first?.value ?? 0)
109     static let nine = Int(Character("9").unicodeScalars.first?.value ?? 0)
110     static let lowercaseCaseA = Int(Character("a").unicodeScalars.first?.value ?? 0)
111     static let lowercaseCaseZ = Int(Character("z").unicodeScalars.first?.value ?? 0)
112     static let capitalCaseA = Int(Character("A").unicodeScalars.first?.value ?? 0)
113     static let capitalCaseZ = Int(Character("Z").unicodeScalars.first?.value ?? 0)
114     static let openBracket = Int(Character("(").unicodeScalars.first?.value ?? 0)
115     static let closeBracket = Int(Character(")").unicodeScalars.first?.value ?? 0)
116     static let openSquareBracket = Int(Character("[").unicodeScalars.first?.value ?? 0)
117     static let closeSquareBracket = Int(Character("]").unicodeScalars.first?.value ?? 0)
118     static let openCurlyBracket = Int(Character("{").unicodeScalars.first?.value ?? 0)
119     static let closeCurlyBracket = Int(Character("}").unicodeScalars.first?.value ?? 0)
120     static let exponent = Int(Character("e").unicodeScalars.first?.value ?? 0)
121     static let plus = Int(Character("+").unicodeScalars.first?.value ?? 0)
122     static let minus = Int(Character("-").unicodeScalars.first?.value ?? 0)
123     static let star = Int(Character("*").unicodeScalars.first?.value ?? 0)
124     static let forwardSlash = Int(Character("/").unicodeScalars.first?.value ?? 0)
125     static let decimal = Int(Character(".").unicodeScalars.first?.value ?? 0)
126 }
127 
128 extension Character {
129 
130     func isAlpha() -> Bool {
131         switch self {
132         case "a"..."z":
133             return true
134         case "A"..."Z":
135             return true
136         default:
137             return false
138         }
139     }
140 
141     func isHexaAlpha() -> Bool {
142         switch self {
143         case "a"..."f":
144             return true
145         case "A"..."F":
146             return true
147         default:
148             return false
149         }
150     }
151 
152     func isNumeric() -> Bool {
153         switch self {
154         case "0"..."9":
155             return true
156         default:
157             return false
158         }
159     }
160 
161     func isAlphaNumeric() -> Bool {
162         return isAlpha() || isNumeric()
163     }
164 
165     func numericValue() -> Int? {
166         guard let unicodeScalar = unicodeScalars.first else {
167             return nil
168         }
169         return Int(unicodeScalar.value) - AsciiValue.zero
170     }
171 
172     var asciiValue: Int {
173         return Int(self.unicodeScalars.first!.value)
174     }
175 }

20ms

 1 class Solution {
 2     func decodeString(_ s: String) -> String {
 3         var strArr = [String]()
 4         var numIndex = 0
 5         
 6         for i in 0..<s.count {
 7             var strItmeIndex = s.index(s.endIndex, offsetBy: -(i + 1))
 8             var strItme = String.init(s[strItmeIndex])
 9             if strItme != "["{
10 
11                 if self.isPurnInt(string: strItme){
12                     var numStr:String = strItme
13 
14                     while  self.isPurnInt(string: strArr.last!){
15                         numStr =  numStr + strArr.last!
16                         strArr.remove(at: strArr.count - 1)
17                     }
18                     if i != s.count - 1{
19                         strArr.append(numStr)
20                     }else{
21                         var strItmeInt:Int = Int(numStr)!
22                         var strNew:String = ""
23                         for j in 0..<strItmeInt{
24                             strNew = strNew + strArr.last!;
25                         }
26                         strArr.remove(at: strArr.count - 1)
27                         strArr.append(strNew)
28                     }
29                     
30                     
31                 }else{
32                     if strArr.count > 0 && self.isPurnInt(string: strArr.last!) {
33                         var strItmeInt:Int = Int(strArr.last!)!
34                         strArr.remove(at: strArr.count - 1)
35                         var strNew:String = ""
36                         for j in 0..<strItmeInt{
37                             strNew = strNew + strArr.last!;
38                         }
39                       strArr.remove(at: strArr.count - 1)
40                       strArr.append(strNew)
41                     }
42                     strArr.append(strItme)
43                 }
44             }else{
45         
46                 var strNew:String = ""
47                 
48                 if strArr.count > 0 && self.isPurnInt(string: strArr.last!) {
49                     var strItmeInt:Int = Int(strArr.last!)!
50                     strArr.remove(at: strArr.count - 1)
51                     for j in 0..<strItmeInt{
52                         strNew = strNew + strArr.last!;
53                     }
54                     strArr.remove(at: strArr.count - 1)
55                     strArr.append(strNew)
56                 }
57                 strNew = ""
58             
59                 while strArr.last != "]"{
60                     strNew = strNew + strArr.last!;
61                     strArr.remove(at: strArr.count - 1)
62                 }
63                 strArr.remove(at: strArr.count - 1)
64                 strArr.append(strNew)
65             }
66         }
67         var result:String = ""
68         for k in 0..<strArr.count{
69             result =  strArr[k] + result
70         }
71        
72         return result
73     }
74     
75     func isPurnInt(string: String) -> Bool {
76         let scan: Scanner = Scanner(string: string)
77         var val:Int = 0
78         return scan.scanInt(&val) && scan.isAtEnd        
79     }
80 }

20ms

 1 class Solution {
 2     func decodeString(_ s: String) -> String {
 3         var nums = [Int]()
 4         var words = [String]()
 5         let chars = Array(s)
 6         var curNum = 0
 7         var result = ""
 8         
 9         for char in s {
10             if char == "[" {
11                 nums.append(curNum)
12                 words.append("")
13                 curNum = 0
14             } else if char == "]" {
15                 var wordToAdd = String(repeating: words.popLast()!, count: nums.popLast()!)
16                 if words.count > nums.count {
17                     wordToAdd = words.popLast()! + wordToAdd
18                 }
19                 
20                 if let prevWord = words.popLast() {
21                     words.append(prevWord + wordToAdd)
22                 } else {
23                     result.append(contentsOf: wordToAdd)
24                 }
25             } else if let num = Int(String(char)) {
26                 curNum = curNum * 10 + num
27             } else {
28                 if nums.count == 0 {
29                     result.append(char)
30                 } else {
31                     let prevWord = words.popLast() ?? ""
32                     words.append(prevWord + String(char))
33                 }
34             }
35         }        
36         return result
37     }
38 }

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原文地址：https://www.cnblogs.com/strengthen/p/10300572.html