给你两个二进制字符串 a 和 b ，以二进制字符串的形式返回它们的和。

思路

  1. 模拟加法
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var addBinary = function (a, b) {
  const items = []
  let inc = 0
  let curIndex = 1
  while (curIndex <= a.length || curIndex <= b.length || inc) {
    let sum = inc
    if (curIndex <= a.length) {
      sum += Number(a[a.length - curIndex])
    }
    if (curIndex <= b.length) {
      sum += Number(b[b.length - curIndex])
    }
    items.push(sum % 2)
    inc = Math.floor(sum / 2)
    ++curIndex
  }
  return items.reverse().join('')
}