leetcode algorithm problem 016 (simple 067) binary summation

• Topic introduction

Given two binary strings, return their sum (expressed in binary).
The input is a non-empty string and contains only numbers 1 and 0.

• Example

• Solution one

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function(a, b) {
  let sum = '', i = 0, flag = '0', longStr = a.length > b.length ? a : b, shortStr = a.length > b.length ? b : a;
  while(i < shortStr.length) {
    if(shortStr[shortStr.length - 1 - i] === longStr[longStr.length - 1 - i]) {
      sum = flag + sum;
      if(shortStr[shortStr.length - 1 - i] === '1') {
        flag = '1';
      } else {
        flag = '0';
      }
    } else {
      sum = (flag === '1' ? '0': '1') + sum;
    }
    i++;
  }
  while(i < longStr.length) {
    let c = longStr[longStr.length - 1 - i];
    if(c !== flag) {
      sum = '1' + sum;
      flag = '0';
    } else {
      sum = '0' + sum;
    }
    i++;
  }
  return flag === '0' ? sum : '1' + sum;
};

• Solution two

/**
 * @param {string} a
 * @param {string} b
 * @return {string}
 */
var addBinary = function(a, b) {
  a = a.padStart(Math.max(a.length, b.length), '0');
  b = b.padStart(Math.max(a.length, b.length), '0');
  let sum = '',
    i = a.length - 1,
    flag = '0';
  while (i >= 0) {
    if (a[i] === b[i]) {
      sum = flag + sum;
      flag = (a[i] === '0' ? '0' : '1');
    } else {
      sum = ((flag === '0' ? '1' : '0') + sum);
    }
    i--;
  }
  return flag === '0' ? sum : '1' + sum;
};

• Be careful