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.
class Solution {
public String addStrings(String num1, String num2) {
int i = num1.length()-1;
int j = num2.length()-1;
int carry = 0;
String res = "";
while(i>=0||j>=0){
if(i>=0){
carry += num1.charAt(i--)-'0';
}
if(j>=0){
carry += num2.charAt(j--)-'0';
}
res = Integer.toString(carry%10) + res;
carry/=10;
}
return carry==0?res:"1"+res;
}
}