Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

The length of both num1 and num2 is < 5100. Both num1 and num2 contains only digits 0-9. Both num1 and num2 does not contain any leading zero. You must not use any built-in BigInteger library or convert the inputs to integer directly.

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings = function(num1, num2) {
    
    //Make sure num1 is the longer string 
    if(num1.length < num2.length){
        var t = num1;
        num1 = num2;
        num2 = t;
    }
    
    //Give a leading zero to make sure num1 is longer even if num1 and num2 have same length
    num1 = ‘0’ + num1;
    num1 = num1.split("").reverse();
    num2 = num2.split("").reverse();
    
    console.log(num1,num2)
    
    
    for(var i=0;i<num1.length;i++){
        var n1 = parseInt(num1[i]);
        var n2 = parseInt((typeof num2[i] == ‘undefined’)?0:num2[i]);
        var t = n1 + n2;
        num1[i] = t % 10;
        if(t >= 10){
            num1[i+1] = parseInt(num1[i+1]) + 1;
        }
    }
    
    if(num1[num1.length-1] == 0){ num1.pop(); }
    num1 = num1.reverse().join(”);
    
    return num1;
    
};