One question that they asked me was a coding question about string and bit manipulation. The question was to sum two strings, where each string was a string of '0's and '1's.

Question

Dmitry · Accepted Answer

class Problem {
    var a: String
    var b: String
    
    init(a: String, b: String) {
        self.a = a
        self.b = b
    }
    
    func solve() {
        var aIndex: String.Index? = a.endIndex
        var bIndex: String.Index? = b.endIndex
        var extraDigit = 0
        var reversed = ""
        while aIndex != nil || bIndex != nil || extraDigit != 0 {
            if aIndex == a.startIndex {
                aIndex = nil
            }
            if bIndex == b.startIndex {
                bIndex = nil
            }
            var aDigit = 0
            if aIndex != nil {
                aIndex = a.index(before: aIndex!)
                let aChar = a[aIndex!]
                aDigit = Int(String(aChar)) ?? 0
            }
            var bDigit = 0
            if bIndex != nil {
                bIndex = b.index(before: bIndex!)
                let bChar = b[bIndex!]
                bDigit = Int(String(bChar)) ?? 0
            }
            if aIndex != nil || bIndex != nil || extraDigit != 0 {
                var resultDigit = aDigit + bDigit + extraDigit
                extraDigit = resultDigit / 2
                resultDigit = resultDigit % 2
                reversed = reversed + String(resultDigit)
            } else {
                break
            }
        }
        if reversed == "" {
            reversed = "0"
        }
        let result = String(reversed.reversed())
        print(result)
    }
}

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