[Swift]LeetCode383. 赎金信 | 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

---

给定一个赎金信 (ransom) 字符串和一个杂志(magazine)字符串，判断第一个字符串ransom能不能由第二个字符串magazines里面的字符构成。如果可以构成，返回 true ；否则返回 false。

(题目说明：为了不暴露赎金信字迹，要从杂志上搜索各个需要的字母，组成单词来表达意思。)

注意：

你可以假设两个字符串均只含有小写字母。

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

---

class Solution {
    func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
        //把英文字符都存入数组中，最后判断数组的每一个位置是否存在<0即可
        var arr = Array(repeating: 0,count:26)
        for index in magazine.indices
        {
            var char:Character = magazine[index]
            for asc in char.unicodeScalars
            {
                var num:Int = Int(asc.value - 97)
                arr[num] += 1
            }
        }
        for index in ransomNote.indices
        {
            var char:Character = ransomNote[index]
            for asc in char.unicodeScalars
            {
                var num:Int = Int(asc.value - 97)
                arr[num] -= 1
                if arr[num] < 0
                {
                    return false
                }
            }
        }
        return true
        
    }
}

---

28ms

class Solution {
    func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
        guard ransomNote.count <= magazine.count else { return false }
        
        var alphabetArray = [Int].init(repeating: 0, count: 26)
        var count = 0
        
        // Add letters from ransomNote to alphabetArray, incrementing count for each letter
        for r in ransomNote.unicodeScalars {
            alphabetArray[Int(r.value) - 97] += 1
            count += 1
        }
        
        // Remove letters from magazine already in alphabetArray, decrementing count for each letter found
        for m in magazine.unicodeScalars {
            if alphabetArray[Int(m.value) - 97]  > 0 {
                // valid existing letter from ransomNote
                alphabetArray[Int(m.value) - 97] -= 1
                count -= 1
            }
            
            // If count == 0, we have a match
            if count == 0 { break }
        }
        
        return count == 0
    }
}

---

52ms

class Solution {
    func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
        var words = [Int](repeating: 0, count: 26)
        let indexChar = "a"
        let indexComp = Int(indexChar.unicodeScalars.first!.value)
        for char in magazine.unicodeScalars {
            let index = Int(char.value) - indexComp
            // var count = words[index] ?? 0
            words[index] += 1
            // words[index] = count
        }
        
        for char in ransomNote.unicodeScalars {
            let index = Int(char.value) - indexComp
            if words[index] <= 0 {return false}
            words[index] -= 1
        }
        return true
    }
}

---

64ms

class Solution {
    func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
        
        var magCounts = Array(repeating: 0, count: 256)
        for each in magazine.utf8{
            magCounts[Int(each)] += 1
        }
        
        for each in ransomNote.utf8{
            if magCounts[Int(each)] == 0 {
                return false
            }else{
                magCounts[Int(each)] -= 1
            }
        }
        
        return true
                
    }
}

---

76ms

class Solution {
    func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
        guard magazine.count >= ransomNote.count else {
            return false
        }
        var magazine = magazine

        for char in ransomNote {
            if let index = magazine.index(of: char) {
                magazine.remove(at: index)
            } else {
                return false
            }
        }

        return true
    }
}

---

84ms

class Solution {
    func canConstruct(_ ransomNote: String, _ magazine: String) -> Bool {
        guard ransomNote.count <= magazine.count else {
            return false
        }
        var magazine = magazine
        for c in ransomNote {
            if let index = magazine.index(of: c) {
                magazine.remove(at: index)
            } else {
                return false
            }
        }
        
        return true
    }
}