[Swift]LeetCode383. 贖金信 | Ransom Note

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Given an arbitrary ransom note string and another string containing letters from all the magazines, write a function that will return true if the ransom note can be constructed from the magazines ; otherwise, it will return false.

Each letter in the magazine string can only be used once in your ransom note.

Note:
You may assume that both strings contain only lowercase letters.

canConstruct("a", "b") -> false
canConstruct("aa", "ab") -> false
canConstruct("aa", "aab") -> true

---

給定一個贖金信 (ransom) 字符串和一個雜誌(magazine)字符串，判斷第一個字符串ransom能不能由第二個字符串magazines裏面的字符構成。若是能夠構成，返回 true ；不然返回 false。

(題目說明：爲了避免暴露贖金信字跡，要從雜誌上搜索各個須要的字母，組成單詞來表達意思。)

注意：

你能夠假設兩個字符串均只含有小寫字母。

canConstruct("a", "b") -> false
canConstruct("aa", "ab") -> false
canConstruct("aa", "aab") -> true

---

 1 class Solution {
 2     func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
 3         //把英文字符都存入數組中，最後判斷數組的每個位置是否存在<0便可
 4         var arr = Array(repeating: 0,count:26)
 5         for index in magazine.indices
 6         {
 7             var char:Character = magazine[index]
 8             for asc in char.unicodeScalars
 9             {
10                 var num:Int = Int(asc.value - 97)
11                 arr[num] += 1
12             }
13         }
14         for index in ransomNote.indices
15         {
16             var char:Character = ransomNote[index]
17             for asc in char.unicodeScalars
18             {
19                 var num:Int = Int(asc.value - 97)
20                 arr[num] -= 1
21                 if arr[num] < 0
22                 {
23                     return false
24                 }
25             }
26         }
27         return true
28         
29     }
30 }

---

28ms

 1 class Solution {
 2     func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
 3         guard ransomNote.count <= magazine.count else { return false }
 4         
 5         var alphabetArray = [Int].init(repeating: 0, count: 26)
 6         var count = 0
 7         
 8         // Add letters from ransomNote to alphabetArray, incrementing count for each letter
 9         for r in ransomNote.unicodeScalars {
10             alphabetArray[Int(r.value) - 97] += 1
11             count += 1
12         }
13         
14         // Remove letters from magazine already in alphabetArray, decrementing count for each letter found
15         for m in magazine.unicodeScalars {
16             if alphabetArray[Int(m.value) - 97]  > 0 {
17                 // valid existing letter from ransomNote
18                 alphabetArray[Int(m.value) - 97] -= 1
19                 count -= 1
20             }
21             
22             // If count == 0, we have a match
23             if count == 0 { break }
24         }
25         
26         return count == 0
27     }
28 }

---

52ms

 1 class Solution {
 2     func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
 3         var words = [Int](repeating: 0, count: 26)
 4         let indexChar = "a"
 5         let indexComp = Int(indexChar.unicodeScalars.first!.value)
 6         for char in magazine.unicodeScalars {
 7             let index = Int(char.value) - indexComp
 8             // var count = words[index] ?? 0
 9             words[index] += 1
10             // words[index] = count
11         }
12         
13         for char in ransomNote.unicodeScalars {
14             let index = Int(char.value) - indexComp
15             if words[index] <= 0 {return false}
16             words[index] -= 1
17         }
18         return true
19     }
20 }

---

64ms

 1 class Solution {
 2     func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
 3         
 4         var magCounts = Array(repeating: 0, count: 256)
 5         for each in magazine.utf8{
 6             magCounts[Int(each)] += 1
 7         }
 8         
 9         for each in ransomNote.utf8{
10             if magCounts[Int(each)] == 0 {
11                 return false
12             }else{
13                 magCounts[Int(each)] -= 1
14             }
15         }
16         
17         return true
18                 
19     }
20 }

---

76ms

 1 class Solution {
 2     func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
 3         guard magazine.count >= ransomNote.count else {
 4             return false
 5         }
 6         var magazine = magazine
 7 
 8         for char in ransomNote {
 9             if let index = magazine.index(of: char) {
10                 magazine.remove(at: index)
11             } else {
12                 return false
13             }
14         }
15 
16         return true
17     }
18 }

---

84ms

 1 class Solution {
 2     func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
 3         guard ransomNote.count <= magazine.count else {
 4             return false
 5         }
 6         var magazine = magazine
 7         for c in ransomNote {
 8             if let index = magazine.index(of: c) {
 9                 magazine.remove(at: index)
10             } else {
11                 return false
12             }
13         }
14         
15         return true
16     }
17 }