intro

计算两个字符串类型num1和num2的数字，并返回num1和num2的和。

Note:

• num1和num2的长度都小于5100
• num1和num2只包含0-9的数字
• num1和num2不包含leading zero
• 不能使用自带的库或者直接转换整形

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

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

思路

• 创建一个while循环，逆序遍历两个数组，当两个数组都遍历完且进位的sum为0的时候跳出循环，在循环中相加两个值

Code (Swift4.0)

func addStrings(_ num1: String, _ num2: String) -> String {    var arr1 = [Int]()    var arr2 = [Int]()    var sumArr = [String]()    for cha in num1.characters {        arr1.append(Int(String(cha))!)    }    for cha in num2.characters {        arr2.append(Int(String(cha))!)    }    var firstIndex = num1.characters.count - 1    var secondIndex = num2.characters.count - 1    var sum = 0    while (firstIndex >= 0) || (secondIndex >= 0) || sum != 0 {        var firstNum = 0        if firstIndex >= 0 {            firstNum = arr1[firstIndex]            firstIndex -= 1        }        var secondNum = 0        if secondIndex >= 0 {            secondNum = arr2[secondIndex]            secondIndex -= 1        }        sum = sum + firstNum + secondNum        sumArr.insert(String(sum%10), at: 0)        sum = sum/10    }    return sumArr.joined()}复制代码

result

Run Time :119ms