题目
给定两个二进制字符串，返回他们的和（用二进制表示）。
输入为非空字符串且只包含数字 1 和 0。
示例 1:
输入: a = "11", b = "1"
输出: "100"
示例 2:
输入: a = "1010", b = "1011"
输出: "10101"
Swift解法
class Solution {
func addBinary(_ a: String, _ b: String) -> String {
let zero = Character("0")
let one = Character("1")
let a = a.map({$0})
let b = b.map({$0})
let count = max(a.count, b.count)
var character = [Character](repeating: zero, count: count)
var i = 0
var flag: UInt8 = 0
while i <= count - 1 {
let aindex = a.count - i - 1
let bindex = b.count - i - 1
let index = count - i - 1
var sum = flag
if aindex >= 0 && a[aindex] == one { sum += 1 }
if bindex >= 0 && b[bindex] == one { sum += 1 }
character[index] = (sum % 2 > 0) ? one : zero
flag = (sum >= 2) ? 1 : 0
i += 1
}
if flag == 1 {
character.insert(one, at: 0)
}
return String(character)
}
}
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/add-binary
