一天一大 leet(字符串相加)难度:简单-Day20200803

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings = function (num1, num2) {
  let len1 = num1.length,
    len2 = num2.length,
    jin = 0, // 进位
    wei = 0, // 本位相加的和
    bu = '',
    result = ''
  // 用0对较小字符串补位
  for (let i = 1; i <= Math.abs(len1 - len2); i++) {
    bu = bu + '0'
  }
  len1 > len2 ? (num2 = bu + num2) : (num1 = bu + num1)
  //   逐位相加 -> 从低位到高位
  for (let i = Math.max(len1, len2) - 1; i >= 0; i--) {
    // 本位相加的和
    wei =
      (parseInt(num1.charAt(i), 10) || 0) +
      (parseInt(num2.charAt(i), 10) || 0) +
      parseInt(jin, 10)

    // 更新结果
    result = parseInt(wei % 10, 10).toString() + result
    // 保留进位
    jin = wei >= 10 ? parseInt(wei / 10, 10) : 0
  }
  //   逐位相加完成还剩余进位则直接拼接到结果上
  return jin > 0 ? jin.toString() + result.toString() : result.toString()
}

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings = function (num1, num2) {
  let i = num1.length - 1,
    j = num2.length - 1,
    jin = 0,
    wei = 0,
    result = ''
  while (i >= 0 || j >= 0 || jin != 0) {
    const x = i >= 0 ? num1.charAt(i) - '0' : 0
    const y = j >= 0 ? num2.charAt(j) - '0' : 0
    wei = x + y + jin
    result = (wei % 10).toString() + result
    jin = parseInt(wei / 10, 10)
    i -= 1
    j -= 1
  }
  return result
}