leetcode_415字符串相加

注意记录进位即可

var addStrings = function(num1, num2) {
    let length1 = num1.length -1
    let length2 = num2.length -1
    let tag = 0
    let result = []
    while(length1 >=0 || length2 >= 0) {
      let first = length1 > -1 ? Number(num1[length1]) : 0
      let second = length2 > -1 ? Number(num2[length2]) : 0
      let temp = first + second + tag
      if(temp >9) {
          tag = 1
          temp = temp - 10
      } else tag = 0
      result.unshift(temp)
      length1--
      length2--
    }
    if(tag == 1) {
        result.unshift(1)
    }
    return result.join('')
};