[Swift]LeetCode415. 字符串相加 | Add Strings

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Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

1. The length of both num1 and num2 is < 5100.
2. Both num1 and num2 contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

---

给定两个字符串形式的非负整数 num1 和num2 ，计算它们的和。

注意：

1. num1 和num2 的长度都小于 5100.
2. num1 和num2 都只包含数字 0-9.
3. num1 和num2 都不包含任何前导零。
4. 你不能使用任何內建 BigInteger 库， 也不能直接将输入的字符串转换为整数形式。

---

class Solution {
    //模拟加法进位
    func addStrings(_ num1: String, _ num2: String) -> String {
        //字符串数组
        var result:[String] = [String]()
        //进位标志
        var carry:Int = 0
        var len1 = num1.count
        var len2 = num2.count
        while(len1 > 0 || len2 > 0 || carry > 0)
        {
            var temp:Int = carry
            if len1 > 0
            {
                len1 -= 1
                var index = num1.index(num1.startIndex,offsetBy: len1)
                var char:Character = num1[index]
                //字符0的ASCII码值 48
                temp = temp + char.toInt() - 48
            }
            if len2 > 0
            {
                len2 -= 1
                var index = num2.index(num2.startIndex,offsetBy: len2)
                var char:Character = num2[index]
                //字符0的ASCII码值 48
                temp = temp + char.toInt() - 48
            }
            carry = temp / 10
            result.append(String(temp % 10))
        }
        //反转数组
        result.reverse()
        //数组转字符串
        return  result.joined(separator: "")
    }
}
    //Character扩展代码  
    extension Character  
    {  
        func toInt() -> Int  
        {  
            var num:Int = Int()
            for scalar in String(self).unicodeScalars  
            {  
                num = Int(scalar.value)  
            }  
            return num  
        }  
    }

---

24ms

class Solution {
    func addStrings(_ num1: String, _ num2: String) -> String {
        
        var chars1 = Array(num1.characters)
        var chars2 = Array(num2.characters)
        
        var i = chars1.count - 1
        var j = chars2.count - 1
        
        var result = ""
        var carry = 0
        
        let val0 = Int(Character("0").unicodeScalars.first!.value)
        
        while i >= 0 || j >= 0 || carry > 0 {
            
            let val1 = i < 0 ? 0 : Int(chars1[i].unicodeScalars.first!.value) - val0
            let val2 = j < 0 ? 0 : Int(chars2[j].unicodeScalars.first!.value) - val0
            
            let sum = val1 + val2 + carry
            
            result = String(sum % 10) + result
            carry = sum / 10
            
            i -= 1
            j -= 1
        }
        
        return result
    }
}

---

28ms

class Solution {
    func addStrings(_ num1: String, _ num2: String) -> String {
        var output = ""
        
        var num1 = Array(num1.utf8.reversed())
        var num2 = Array(num2.utf8.reversed())
        
        var num1Index = 0
        var num2Index = 0
        
        var c: UInt8 = 0
        
        while num1Index < num1.count,
              num2Index < num2.count {
            let n1 = num1[num1Index]
            let n2 = num2[num2Index]
                
            let v = (n1 - 48) + (n2 - 48) + c
            
            output.append(String(v % 10))
            c = v / 10
                
            num1Index += 1
            num2Index += 1
        }
        
        while num1Index < num1.count {
            let n1 = num1[num1Index]
            let v = (n1 - 48) + c
            
            output.append(String(v % 10))
            c = v / 10
            
            num1Index += 1
        }
        
        while num2Index < num2.count {
            let n2 = num2[num2Index]
            let v = (n2 - 48) + c
            
            output.append(String(v % 10))
            c = v / 10
            
            num2Index += 1
        }
        
        if c != 0 {
            output.append(String(c))
        }
        
        return String(output.reversed())
    }
}

---

32ms

class Solution {
    private let charToInt : [Character : Int] = [
        "0" : 0, "1" : 1, "2" : 2, "3" : 3, "4" : 4,
        "5" : 5, "6" : 6, "7" : 7, "8" : 8, "9" : 9
    ]
    
    func addStrings(_ num1: String, _ num2: String) -> String {
        let chars1 = Array(num1.characters)
        let chars2 = Array(num2.characters)
        var i = chars1.count - 1
        var j = chars2.count - 1
        var carry : Int = 0, sum : Int = 0
        var rlt: String = ""

        while i >= 0 || j >= 0 {
            let n1 = i >= 0 ? charToInt[chars1[i]] : 0
            let n2 = j >= 0 ? charToInt[chars2[j]] : 0
            sum = n1! + n2! + carry
            carry = sum / 10
            rlt = "(sum % 10)" + rlt
            i -= 1
            j -= 1
        }
        if carry > 0 { // check the last carry for entire string;
            rlt = "(carry)" + rlt
        }
        return rlt
    }
}

---

36ms

class Solution {
    func addStrings(_ num1: String, _ num2: String) -> String {
        var it1 = num1.count - 1
        var it2 = num2.count - 1
        var nn1 = Array(num1)
        var nn2 = Array(num2)
        var rem = 0
        var res: String = ""
        
        while it1 >= 0 || it2 >= 0 {
            defer { it1 -= 1; it2 -= 1 }
            let d1 = it1 >= 0 ? (toNum(nn1[it1]) ?? 0) : 0
            let d2 = it2 >= 0 ? (toNum(nn2[it2]) ?? 0) : 0
            let num = rem + d1 + d2
            res.append(toChar(num % 10))
            rem = num / 10
        }
        if rem > 0 {
            res.append("1")
        }
        return String(res.reversed())
    }
    
    let chDigits = ["0":0,"1":1,"2":2,"3":3,"4":4,"5":5,"6":6,"7":7,"8":8,"9":9]
    let digitsCh = [0:"0",1:"1",2:"2",3:"3",4:"4",5:"5",6:"6",7:"7",8:"8",9:"9"]
    
    func toNum(_ char: Character) -> Int? {
         return chDigits[String(char)]
    }
    
    func toChar(_ n: Int) -> String {
        return digitsCh[n]!
    }
}

---

36ms

class Solution {
    func addStrings(_ num1: String, _ num2: String) -> String {
        var result = ""
        
        var arr1: [UnicodeScalar] = num1.unicodeScalars.reversed()
        var arr2: [UnicodeScalar] = num2.unicodeScalars.reversed()
        var carry = 0
        var index = 0
        
        while index < arr1.count || index < arr2.count {
            var n1 = 0
            var n2 = 0
            
            if index < arr1.count {
                let ch1 = arr1[index]
                n1 = Int(ch1.value) - Int("0".unicodeScalars.first!.value)
            }
            if index < arr2.count {
                let ch2 = arr2[index]
                n2 = Int(ch2.value) - Int("0".unicodeScalars.first!.value)
            }
            
            let sum = n1 + n2 + carry
            result = String(sum % 10) + result
            carry = sum / 10
            index += 1
        }
        
        if carry > 0 {
            result = String(carry) + result
        }
        
        return result
    }

}

---

44ms

class Solution {
    func addStrings(_ num1: String, _ num2: String) -> String {
        
        let nums1 = Array(num1.characters).map { 
            Int($0.unicodeScalars.first!.value - Character("0").unicodeScalars.first!.value)
        }
        let nums2 = Array(num2.characters).map { 
            Int($0.unicodeScalars.first!.value - Character("0").unicodeScalars.first!.value)
        }

        var i = nums1.count - 1
        var j = nums2.count - 1
        var carry = 0
        var result = ""
        
        while i >= 0 || j >= 0 || carry > 0 {
            
            let num1 = i >= 0 ? nums1[i] : 0
            let num2 = j >= 0 ? nums2[j] : 0
            
            let sum = num1 + num2 + carry
            result = String(sum % 10) + result
            carry = sum / 10
            
            i -= 1
            j -= 1
        }
        
        return result
    }
}

---

44ms

import Foundation

class Solution {
    
    func addStrings(_ num1: String, _ num2: String) -> String {
        var result = ""
        
        var arr1: [UnicodeScalar] = num1.unicodeScalars.reversed()
        var arr2: [UnicodeScalar] = num2.unicodeScalars.reversed()
        var carry = 0
        var index = 0
        
        while index < arr1.count || index < arr2.count {
            var n1 = 0
            var n2 = 0
            
            if index < arr1.count {
                let ch1 = arr1[index]
                n1 = Int(ch1.value) - Int("0".unicodeScalars.first!.value)
            }
            if index < arr2.count {
                let ch2 = arr2[index]
                n2 = Int(ch2.value) - Int("0".unicodeScalars.first!.value)
            }
            
            let sum = n1 + n2 + carry
            result = String(sum % 10) + result
            carry = sum / 10
            index += 1
        }
        
        if carry > 0 {
            result = String(carry) + result
        }
        
        return result
    }
}