add-string/index.js

Add 2 Strings

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */

var addStrings = function(num1, num2) {
    let arr1 = num1.split("");
    let arr2 = num2.split("");
    arr1.unshift(0);
    arr2.unshift(0);
    if (arr1.length > arr2.length) {
      arr2.unshift(...Array(arr1.length - arr2.length).fill(0));
    } else {
      arr1.unshift(...Array(arr2.length - arr1.length).fill(0));
    }
    let len = arr1.length;
    let carryOverArray = Array(len).fill(0);
    let resArray = Array(len).fill(0);
    let sum;
    for (let i = len - 1; i >= 0; i--) {
      sum = +arr1[i] + +arr2[i] + carryOverArray[i];
      if (sum >= 10) {
        carryOverArray[i - 1] = 1;
        resArray[i] = sum - 10;
      } else {
        resArray[i] = sum;
      }
    }
    let resultStr = resArray.join("");
    if (resultStr.charAt(0) === "0") resultStr = resultStr.substr(1);
    return resultStr;
  };
  
  
  module.exports = addStrings;