LeetCode problem 67. Given two binary strings a and b, return their sum as a binary string.

67_Add_Binary.swift

class Solution {
    func addBinary(_ a: String, _ b: String) -> String {
        var result = ""
        
        let aStrArr = Array(String(a.reversed())).map{ String($0) }
        let bStrArr = Array(String(b.reversed())).map{ String($0) }
        
        var index = 0
        var advanced = 0
        while index < aStrArr.count && index < bStrArr.count {
            if aStrArr[index] == "1" && bStrArr[index] == "1" {
                if advanced == 1 {
                    result = result + "1"
                    advanced = 1
                }
                else {
                    result = result + "0"
                    advanced = 1
                }
            }
            else if aStrArr[index] == "0" && bStrArr[index] == "0" {
                if advanced == 1 {
                    result = result + "1"
                    advanced = 0
                }
                else {
                    result = result + "0"
                    advanced = 0
                }
            }
            else {
                if advanced == 1 {
                    result = result + "0"
                    advanced = 1
                }
                else {
                    result = result + "1"
                    advanced = 0
                }
            }
            
            index += 1
        }
        
        let remainingArr = (index < aStrArr.count) ? aStrArr : bStrArr
        
        while advanced == 1 {
             if index < remainingArr.count {
                if remainingArr[index] == "0" {
                    result = result + "1"
                    advanced = 0
                }
                else {
                    result = result + "0"
                    advanced = 1
                }
            }
            else {
                result = result + "1"
                advanced = 0
            }
            
            index += 1
        }

        while index < remainingArr.count {
            result = result + remainingArr[index]
            index += 1
        }
        
        
        return String(result.reversed())
    }
}